PRAM Gremlins

The PRAM or Parameter RAM in a Mac is a small chunk of RAM that is maintained from one start-up to the next. It holds settings like the video depth and resolution, and a number of System settings. It occasionally gets corrupt, and can cause seemingly random crashes.

To reset the PRAM, hold down Command, Shift, P and R while starting up. Your Mac will start up, pause and then restart. Release the keys and let it start-up normally after that.