Try doing PRAM and NVRAM reset. Below are instructions from Apple.
1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.
Did you try Safe Boot? Start up your Mac while holding down the Shift key.
Also, try running the Apple Hardware Test by booting from Install DVD 1 (insert disc, reboot with the d key pressed).
my mac book pro was working fine this morning and when i opened it up again in the afternoon the screen was not working. I tried restarting several times and the machine itself makes all the typical sounds an chimes but nothing on the screen. Someone suggested i may have to reset the video ram?
