At restart or at Start up before the chime hold down the Command and Option keys until you are asked if you are sure you want to rebuild the Desktop. Click Yes.

Zapping the PRAM: Clearing your RAM for faster processing. You may need a friend to help!

At restart or at Start up before the chime hold down the Command, Option, P and R keys until you hear 2 chimes let go and your computer will boot up like normal.

Force Quit: If you just can't get a program to respond.

Hold down the Command, Option and hit the Esc key and click on Force Quit. Save all that you can and Restart your computer.

Forced Restart: When you just can't do anything including the Forced Quit.

Hold down the Command, Control and Power keys.

You will need to set up a schedule to do the maintenance regularly and not just when your computer is on the blink. You may want to try and schedule it in after your regular backup. I hope this information will help you to maintain your computer and keep it running smoothly