Anything else to try for Sleep Light but no screen?

I have a 2.4Ghz Macbook Unibody Aluminum.

After pushing the power button while the computer is turned off, the sleep light turns on, the fans spin, the cd drive spins (there is a disk in the drive). I believe the hard drive spins too. The computer does this for about 15 seconds and then abruptly shuts off. If I press the power button again the computer does all the same things except it doesn't shut off and spins for as long as i'll leave it on.

During all of this the screen does not come on at all. I have held a flash light up to it and I can see nothing so I'm guessing not the backlight either. No startup chimes. I don't even know if the PRAM reset goes through.

I have tried:

1. Reseting PRAM and PMU

2. Using different RAM, trying one in each slot at a time, and using the original RAM, one in each slot each time.

3. Compressed Air spraying the RAM sockets.

What else should I try before I conclude it's the logic board/GPU?

Thanks!