Mac OS X 10.6: Starting up in safe mode
Starting up in “safe mode” may help you to diagnose problems you’re having with your computer.
To start up in safe mode:
Shut down your computer and wait 10 seconds.
Press the power button.
Immediately after you hear the startup tone, hold down the Shift key.
You should press the Shift key as soon as possible after you hear the startup tone, but not before.
Release the Shift key when you see the gray Apple logo and progress indicator (spinning gear).
To leave safe mode, restart the computer normally without holding down any keys during startup.