Mac Classic Tips
The following tips will get you most crashes, if you have an older machine and are running OS 7,8, or 9, or even if you're running Mac OS Classic under OS X.
Resetting OPEN Firmware
Restart the computer, immediately hold down the Apple, Option, O, and F keys simultaneously and keep them held down. A command prompt will come up. Type in "reset-nvram", press return, then type in "reset-all", and press return. The computer will restart and hopefully boot up normally.
Zapping the PRAM
Restart the computer, immediately hold down the Apple, Option, P, and R keys simultaneously and keep them held down. As long as you hold down these keys during startup, the computer will go through a startup cycle with the characteristic Macintosh startup chime. Hold down the keys until you hear at least 6 startup chimes, then let go of the keys. The computer will restart and hopefully boot up normally.
Rebuilding the Desktop
Restart the computer, immediately hold down the Apple and Option keys, and keep them held down until you get a windows that says "Are you sure want to rebuild the desktop on [Macintosh HD]". Press Okay button and let the machine rebuild the desktop file. Note: if you're operating in Classic mode, you can rebuild the desktop in the Classic Startup preferences panel in System Preferences.
Disable Extensions
Restart the computer, immediately hold down the Shift key. The computer will start up with a message in the startup window that says Extensions Disabled.
Rebuild the Disk Directory
Purchase a copy of DiskWarrior from AlSoft. This is THE utility used by everybody to optimize and even resurrect dead drives. An absolute must-buy for every Macintosh User.