Troubleshooting Boot-Time Error Messages
The BIOS performs a power-on self-test (POST) when it starts up the system, to check out the PC and make sure that everything is working properly. Assuming that the BIOS is able to boot the system far enough to gain access to the video subsystem, it will display information about the PC as it boots. It will also use the video system to communicate error messages to the user. In fact, most boot problems are displayed via video error messages, as opposed to audio beep codes.
An error message can be produced by various different parts of the system, depending on how far into the boot process the system gets before it is produced. Most error messages are produced by the system BIOS, as it is responsible for most of the functions of starting the boot. However, other error messages are operating-system-specific.
There are many thousands of individual error messages; some are more common than others because there are only a few different BIOS companies that are used by the majority of PCs out there today. However, since the exact wording of an error message can be changed by the manufacturer of each system or motherboard, there are a lot of variations.
In most cases, the messages are pretty similar to each other; you may see a slightly different wording in your error message than the ones I have listed here, but if the messages look substantially the same, it is probably safe to follow the diagnosis here. "Disk drive failure" and "Diskette drive failure" are what I mean by virtually identical messages. You may want to consult with your owner's manual regarding some unusual messages, or to ensure that your manufacturer means the same thing with their messages that other companies do (there is some strange stuff "out there").
Please note that similar error messages, those that really mean the same thing but just use different wording, have their descriptions and diagnoses grouped together to make things simpler. There is not a one-to-one correspondence between the error messages listed in the index frame on the left, and the diagnoses shown below. It is best to use the index frame to select the error message you are seeing.
Some additional notes:
I have listed all the error messages on the left strictly alphabetically, in the hopes that this makes it easier for you to find what you are looking for than having them in categories.
I have converted all error messages to mixed case, for consistency. Some PCs use ALL CAPS for their error messages (which is hard on the eyes anyway) and some do not.
Errors indicating failure related to A20 line
Explanation: The system is detecting a failure trying to access the 21st address line, A20. This line is used to provide access to the high memory area, and is normally controlled through the keyboard controller.
Diagnosis: This is usually a problem with either the keyboard or the keyboard controller on the motherboard.
Recommendation:
Detected short in address line
Explanation: The system has detected a short-circuit in one or more of the lines of the address bus on the motherboard.
Diagnosis: This is usually a motherboard failure or related problem.
Recommendation: Treat as a motherboard failure.
BIOS ROM Checksum Errors
Explanation: The read-only memory (ROM) containing the BIOS program is protected by a checksum value as a double-check that the ROM code is correct. This checksum is compared against the values in the ROM each time the PC is booted and if there is a mismatch, this code is generated.
Note: This error is not the same as a CMOS Checksum Error, which refers
to corrupted values of the CMOS settings, the ones you set through the BIOS setup program.
This error means the contents of the BIOS code itself are damaged.
Diagnosis: The BIOS ROM chip on the motherboard is probably faulty. It could also be another component on the motherboard.
Recommendation: Troubleshoot the motherboard.
Level 2 cache failure
Explanation: Some BIOSes perform tests on the level 2 or secondary cache to ensure that it is functioning correctly. The level 2 cache in the system is indicating a failure. Depending on the system, the boot may halt here or the system may automatically disable the cache and continue with the boot; the exact message you get should give you a hint about this.
Diagnosis: There is either a problem with the secondary cache itself, or with the motherboard.
Recommendation:
Timer errors
Explanation: There is an error being reported with one of the system timers on the motherboard.
Diagnosis: This is usually a motherboard or system device problem.
Recommendation: Troubleshoot the motherboard
CMOS battery failure
Explanation: The CMOS memory holds the BIOS settings that you define in the BIOS setup program. This memory is powered using a battery so that the settings are not lose when you turn off the power to the system. Many motherboards do not test the status of this battery and will just indicate problems with the CMOS memory when the battery fails, but some motherboards can detect when the battery is no longer functioning.
Diagnosis: The CMOS battery has probably failed, if the system was previously working; if it is a new system, this could be a motherboard problem.
Recommendation: Troubleshoot the battery
CMOS battery low
Explanation: The CMOS memory holds the BIOS settings is powered using a battery so that the settings are not lost when the PC is turned off. Some motherboards can detect when the battery is getting weak (though many do not). The system is giving you a warning that the battery is getting low on power.
Diagnosis: The battery is running low. It is unusual for this to be caused by anything else.
Recommendation: Follow these directions to deal with the failing battery. You should still be able to use the system without any problems for a while.
CMOS checksum errors
Explanation: A checksum is computed as an error-detecting code, to protect the BIOS
settings stored in
the CMOS memory. Each time the system is booted this number is recomputed and checked
against the
stored value. If they do not match, an error message is generated to tell you that the
CMOS memory
contents may have been corrupted and therefore some settings may be wrong. BIOSes react in
different
ways to encountering this sort of error. Some will warn the user and then continue on with
whatever
settings were in the CMOS. Others will assume that the settings that were in the CMOS were
corrupted
and will load default values stored in the BIOS chip "for safety reasons". The
error message will indicate
which your system is doing.
Diagnosis: The most common cause of checksum errors in CMOS is a battery that is losing
power. Viruses
can also affect CMOS settings, and motherboard problems can also affect the stored values.
Recommendation: Follow the instructions in this section to address the CMOS corruption.
You should
make sure that all of the BIOS settings in the system are correct, by rebooting the
system, going into BIOS
setup and double-checking all the values (hopefully against a recent BIOS settings
backup).
CMOS display type mismatch
Explanation: The system has detected that the type of video card you have in the PC is not
the same as
the one you told the system you had.
Diagnosis: The BIOS setting that controls the display type for the PC is set incorrectly.
Very rarely, there
could be some other bizarre explanation for this problem.
Recommendation:
Double-check and correct the video display type BIOS setting. It should be set to
"VGA" or "VGA/EGA"
for virtually all newer PCs.
Troubleshoot the video card if the BIOS setting is correct and this problem persists.
Troubleshoot the motherboard.
CMOS display type mismatch
Explanation: The system has detected that the type of video card you have in the PC is not
the same as
the one you told the system you had.
Diagnosis: The BIOS setting that controls the display type for the PC is set incorrectly.
Very rarely, there
could be some other bizarre explanation for this problem.
Recommendation:
Double-check and correct the video display type BIOS setting. It should be set to
"VGA" or "VGA/EGA"
for virtually all newer PCs.
Troubleshoot the video card if the BIOS setting is correct and this problem persists.
Troubleshoot the motherboard.
CMOS memory size mismatch
Explanation: Some PCs store the total amount of memory as a BIOS setting and then compare
the value
against what they detect in hardware when the PC is booted. A message is produced when the
system
sees a different amount of memory than what it was expecting. Most newer PCs do not bother
with this
but just use what they detect when the machine is powered up.
Diagnosis: Depending on the circumstances, this may not really be an error message at all.
Many systems
will produce this message the first time that they are booted after a memory addition or
subtraction, and
then the problem will go away thereafter. If this problem is occurring repeatedly, or
after no change in
memory, then there may be a problem.
Recommendation: Enter the BIOS setup program and verify that it now shows the correct
amount of
memory. If your BIOS requires you to enter the memory total, make sure you specify the
correct amount
of memory in the system. Then reboot the PC; the message should not return. If it does,
then you should
treat this as a corrupted CMOS problem.
CMOS information invalid
Explanation: The BIOS has detected that one or more of the setting parameters it has read
from the
CMOS memory is invalid.
Diagnosis: If this occurs in an existing system, it generally means that the contents of
the CMOS memory
have become corrupted. It is normal to get an error of this sort when you boot some kinds
of new
motherboards for the first time, since they have never been set up before.
Recommendation: For a new system, enter BIOS setup and make sure to set and save
parameters. Then
reboot, and the problem should go away. For an existing system, troubleshoot as a
corrupted CMOS
problem.
CMOS date and time not set
Explanation: The system has detected that the date and time stored in the CMOS memory were
never set
up.
Diagnosis: This is normal upon booting many types of new motherboards for the first time.
If it happens
with an existing system it usually means that the CMOS memory has been corrupted or
cleared somehow.
Recommendation: For a new system, enter BIOS setup and make sure to set the date and time.
Double-check the other settings for accuracy, and save the settings and exit. Then reboot,
and the
problem should go away. For an existing system, if this problem persists, troubleshoot as
a corrupted
CMOS problem.
CPU at XXX
Explanation: The system is reporting the speed of the processor.
Diagnosis: The system is behaving normally, as long as it continues to boot and doesn't
halt when this
message is displayed.
Recommendation: No action is required; this is an informational message only. If the speed
of the
processor being reported is incorrect based on what the speed is supposed to be, continue
here.
No boot device
Explanation: The system has attempted to find a drive to boot the operating system, but
has failed (the
error message itself may not always be very clear that this is what has happened,
especially the infamous
"NO ROM BASIC - SYSTEM HALTED"; see here for more on that error.) The system
cannot start up because
there is no operating system for it to load. The boot process will halt here. Some systems
may give you
the option to retry the boot or to enter setup at this point, as a convenience. Otherwise,
you must reboot
the PC.
Diagnosis: All of the bootable drives in the system are not functioning. Normally this
means that the
floppy disk drive is either absent or not functioning, or has no disk in it, and the hard
disk is either not
connected or has no bootable active partition on it.
Recommendation:
If this is a new system with a hard disk that has never been formatted before, you need to
boot
from a floppy first, and partition and format the hard disk. Try that.
If you were trying to boot from the floppy disk drive, troubleshoot the floppy disk drive.
If you were trying to boot from the hard drive, troubleshoot the hard disk drive.
Floppy disk failure
Explanation: One or more of the floppy disk drives in the system has been reported as
either failing or
missing by the BIOS as the system is booted. The BIOS may identify the specific drive in
some cases.
Diagnosis: This error message implies a device failure of the floppy disk drive or a
related problem.
Recommendation: Troubleshoot the floppy disk drive(s).
Floppy drive mismatch
Explanation: The system has detected that the type of floppy disk drives it sees in the
system does not
match what you have defined in the BIOS setup program. In fact, many systems will not
report this but
will just malfunction when the drive(s) are set up incorrectly.
Diagnosis: The floppy disk settings in the BIOS setup are incorrect.
Recommendation:
Enter the BIOS setup program and correct the floppy disk type settings.
Troubleshoot the floppy disk drive(s). In particular, ensure that the floppy disk drives
are connected
properly; they may be cabled backwards if you are using two drives.
Display adapter failed, using alternate
Explanation: Some systems have the ability to support a primary and a secondary video
display (the
secondary typically being monochrome text). The system has detected a failure in the
primary display and
therefore is using the secondary one.
Diagnosis: The BIOS setting for display type may be set wrong, or there may be a failure
of the video
card.
Recommendation:
Double-check the video display type BIOS setting.
Troubleshoot the video card.
Display switch is set incorrectly
Explanation: Some older PCs have a switch on the motherboard that can be toggled between
"monochrome" and "color", instead of having a BIOS setting to control
display type. The system has
detected a mismatch between this setting and the video card it is seeing in the PC.
Diagnosis: The display switch is set incorrectly, there is a video card problem, or there
is a motherboard
problem.
Recommendation:
Check your system manual to find out if you have a display type switch, and if you do,
make sure it
is set correctly.
Troubleshoot the video card.
Troubleshoot the motherboard.
Display type has changed since last boot
Explanation: The system has detected that the display type has changed since the last time
the PC was
booted. There is a mismatch between what the video card is in the PC and what the setting
for the video
card is in the BIOS CMOS memory.
Diagnosis: This is probably not really a problem condition, but a notification that the
video card has
changed but the BIOS setting for it hasn't been updated. The BIOS setting should be
changed to reflect the
new display.
Recommendation:
Enter the BIOS setup program and adjust the display type setting so it is correct.
If the display type is already set correctly, troubleshoot the video card.
Troubleshoot the motherboard.
DMA Errors
Explanation: The system has detected an error associated with the direct memory access
(DMA)
controller(s) on the system motherboard.
Diagnosis: This is most likely a motherboard problem, but it might be caused by a bad
expansion card as
well. If the DMA controller number is supplied as part of the error message, that might
help narrow down
the DMA channel where the problem was detected, if applicable. DMA controller #1 handles
DMA channels
0 to 3, and controller #2 handles channels 5 to 7 (channel 4 is the cascade between the
two controllers).
Recommendation:
Troubleshoot as a generic expansion card issue.
Troubleshoot the motherboard.
DMA Bus Time-out
Explanation: A device in the system has attempted to keep control of the DMA bus for an
excessive
period of time. Some systems will generate an error condition under these circumstances.
Diagnosis: This is most likely a problem with an expansion device or with the motherboard
itself.
Recommendation:
Troubleshoot as a generic expansion card issue.
Troubleshoot the motherboard.
Error with Hard Disk
Explanation: The system has detected a failure with one or more of the IDE/ATA hard disk
drives in the
system. The problem report may highlight a specific device ("drive 0" or
"primary master") depending on
the BIOS type.
Diagnosis: This is usually a problem related to the hard disk(s) themselves; this may not
mean that the
hard disk is bad, but could mean incorrect cabling or another issue making it impossible
to find the hard
disk. The controller or interface to the hard disk could also be at fault.
Recommendation:
Troubleshoot the hard disk drive.
Troubleshoot the hard disk controller.
Error with hard disk controller
Explanation: The system has detected a failure related to the IDE hard disk controller. The controller is a separate I/O card that plugs into the motherboard on older systems. Newer PCs have the controller built into the motherboard.
Diagnosis: This is usually a problem related to the hard disk controller, of course, but it could also be the hard disk(s) themselves.
Recommendation:
Memory access failures
Explanation: A failure was detected within the system memory. This usually means a failure of the simple memory tests performed at boot time, which generally consist of writing a pattern to memory and reading it back to ensure that it has not changed. Depending on the system, you may be told some specifics about what part of memory failed.
Diagnosis: There are many possible root causes for this problem, usually associated with the system memory. There could be a motherboard problem as well.
Recommendation:
Floppy disk controller failures
Explanation: The system has detected a failure related to the floppy disk controller. The controller is a separate I/O card that plugs into the motherboard on older systems. Newer PCs have the controller built into the motherboard.
Diagnosis: This is usually a problem related to the floppy disk controller, but could also be the floppy disk(s) themselves. It can be caused by telling the BIOS that there are floppy disk drives in the system when there are not.
Recommendation:
Hard disk CMOS mismatch
Explanation: Some systems will automatically examine the IDE hard disk(s) in the system and compare its/their geometry to the parameters entered for it in the BIOS settings. If the values do not match this message may be generated.
Diagnosis: The usual cause of this message is changing the hard disk drive and forgetting to change the hard disk settings in the BIOS setup program. Otherwise it could indicate a hard disk or controller problem.
Recommendation:
Hard disk initializing; please wait a moment...
Explanation: In the early days of PCs, it took a long time to boot the system. PCs have gotten much faster and people have started to want their machines to boot in less time. As a result, some PCs now boot up so quickly that they try to autodetect the hard disks, or even boot the operating system from the hard disk, before the hard disk is ready to go. This can cause apparent failures with the hard disk if the situation is not detected. When this message appears, the system is being smart enough to detect this condition and wait for the hard disk to respond.
Diagnosis: The system is behaving normally, as long as it continues to boot and doesn't halt when this message is displayed.
Recommendation: No action is required if the boot proceeds normally. If the system hangs after displaying this message, you should treat this as a hard disk problem.
I/O card parity error
Explanation: An expansion card has generated an error indicating incorrect operation.
Diagnosis: This is most probably an expansion card problem, particularly if it is associated with only one expansion card in a system in which others are working properly.
Recommendation:
Level 1 cache failure
Explanation: The BIOS has tested and determined that the processor's internal cache is not functioning correctly, and has disabled it.
Diagnosis: This is a very unusual situation, for the internal cache to be not functional while the rest of the processor is. This is likely a processor or motherboard problem.
Recommendation:
Interrupt Controller failures
Explanation: The system has detected an error associated with the interrupt controller(s) on the system motherboard.
Diagnosis: This is most likely a motherboard problem, but it might be caused by a bad expansion card as well. If the interrupt controller number is supplied as part of the error message, that might help narrow down the interrupt request line where the problem was detected, if applicable, although IRQ controller #1 handles all of the IRQs, some directly and others indirectly via controller #2. IRQ controller #2 handles IRQs 8 through 15.
Recommendation:
Invalid media type
Explanation: The system tried to use a disk or other media that is of the incorrect type.
Diagnosis: This is one of those poorly-phrased messages; what it almost always means is that you tried to use a hard disk volume after partitioning it but before formatting it. For example, if you are setting up a new system and you partition the hard disk, then boot from a floppy and type "DIR C:", you will usually get this message. The system looks for the media type descriptor on the hard disk and doesn't find what it expects, and produces this message.
Recommendation:
Invalid partition table
Explanation: The system examined the master partition table to determine what volume to use to boot the operating system, and found invalid information within it.
Diagnosis: You should never see this message under normal circumstance. One way that this message can occur is if more than one partition is set "active" or bootable; only one is allowed to be at a time. It is possible that the master partition table has become corrupted.
Recommendation:
Keyboard clock line failure
Explanation: The clock line is one of the control lines between the keyboard and the keyboard controller that interfaces the keyboard to the motherboard.
Diagnosis: There is a problem either with the keyboard or with the keyboard controller on the motherboard.
Recommendation:
Keyboard data line failure
Explanation: The data line is one of the control lines between the keyboard and the keyboard controller that interfaces the keyboard to the motherboard.
Diagnosis: There is a problem either with the keyboard or with the keyboard controller on the motherboard.
Recommendation:
Keyboard failure
Explanation: The system has detected what appears to be a failure with the keyboard.
Diagnosis: Usually this is a problem with the keyboard, such as it being disconnected from the PC, having a key stuck down on it, and so forth. Could also be the keyboard controller.
Recommendation:
Keyboard key stuck
Explanation: A key was stuck on the keyboard as the system booted up. Some systems will detect this specifically, while others just give a generic "Keyboard error" in this situation. Some systems will produce a two-digit code when this error occurs, which tells you the scan code of the key that is causing the problem. This may let you correct it more easily.
Diagnosis: Usually this error occurs from trying to type on the keyboard while booting. If this is not the problem it is usually a keyboard problem.
Recommendation:
Key lock locked
Explanation: The system is detecting that the key lock on the front of the case is locked, and therefore will not boot. The error message usually refers to the keyboard being locked but this really means the key lock on the front of the system case.
Diagnosis: The key lock may be indeed locked out. The key lock may also be miswired, or there could be a fault with the motherboard, or even the keyboard.
Recommendation:
Keyboard key stuck
Explanation: A key was stuck on the keyboard as the system booted up. Some systems will detect this specifically, while others just give a generic "Keyboard error" in this situation. Some systems will produce a two-digit code when this error occurs, which tells you the scan code of the key that is causing the problem. This may let you correct it more easily.
Diagnosis: Usually this error occurs from trying to type on the keyboard while booting. If this is not the problem it is usually a keyboard problem.
Recommendation:
Memory test message
Explanation: The system is testing the system memory.
Diagnosis: The system is behaving normally, as long as it continues to boot and doesn't halt when this message is displayed.
Recommendation: No action is required; this is an informational message only.
Override enabled - Defaults loaded
Explanation: The system found that the current BIOS settings in the CMOS memory are invalid, and so it loaded the default settings that are stored in the BIOS ROM chip.
Diagnosis: This error message usually means that the contents of the CMOS memory have become corrupted
Press F1 to disable NMI, F2 to reboot
Explanation: Some low-level hardware problems cause the generation of a non-maskable interrupt, or NMI. The most common example is a parity error. This interrupt causes all processing to immediately cease so the error condition can be handled. Some systems, when this situation is detected, will give you the option of disabling the NMI signal and continuing on, or rebooting the machine (while others will just halt the system and force you to do a hardware reset). This error message should always be encountered with another error message before it, which states what the cause of the NMI was.
Diagnosis: This message itself is informational and is not an error message (the message it comes with is the error message).
Recommendation: Address the problem by diagnosing the error message that caused the NMI.
Warning: Disabling NMI will cause the system to keep booting, ignoring the error
condition. This can lead to unpredictable results and is not recommended.
Shutdown failure
Explanation: The system is detecting a failure on the motherboard related to the shutdown or reset logic.
Diagnosis: This is an unusual error and implicates the motherboard.
Recommendation: Troubleshoot the motherboard.
Static Resource Conflict
Explanation: The BIOS is detecting that two different hardware components in the PC are trying to use the same system resource (IRQ line, DMA channel or I/O address).
Diagnosis: This may or may not actually be a problem with the system. The system thinks that two devices are conflicting, but in some cases the conflict is actually between one device and itself, or between two devices that seem to be in conflict but really are not.
Recommendation: Troubleshoot this problem here
Unexpected interrupt in protected mode
Explanation: The system has detected an interrupt that should not be occurring within the system.
Diagnosis: This is probably either a processor or motherboard problem.
Recommendation:
Updating ESCD...
Explanation: ESCD stands for "extended system configuration data", and is where resource information is stored on a system that uses Plug and Play. This message is displayed when the system detects a change in the hardware configuration and therefore updates the Plug and Play information that it has stored. In some systems it may appear every time the PC is booted, however, even if the hardware configuration has not changed.
Diagnosis: Depending on the circumstances, this message may indicate an error or a normal operating condition.
Recommendation: