


It can repair the directory without wiping out all the contents of the hard drive. That program has saved my backside many times. While reinstalling the OS can help this, you should try DiskWarrior first. There could also be a hard drive directory issue. You have to hold down the shift key until you see something like "safeboot" on the startup screen (not the grey screen, but the next one.) This causes the mac to boot into safe mode. If it still does not boot up, try booting up with the shift key held down. Do NOT LET UP ON THE KEYS until you hear the bong four times.

Keep holding down these keys until you hear the "bong" four times. Hold down the command-option-p-r keys, and turn on the computer. SOURCE: My iMac G4 turns on and goes to the grey startup
