I have a 2007 2.4Ghz macbook pro with a nvidia 8600gt So the computer was on for 3 days straight, in the final hours things became slow, the network transfer rates slowed to a crawl, programs became slow and etc. I decided to restart my computer. Saved all my apps, It shut down and never booted up again! I hit the power button, the sleep light goes on (steady light), fan comes on at full speed, hard drive spins. There is no start up chime, the screen is not on, backlit not even on. Backlit board not on either. I know the light sensor works because when i cover them, the sleep light becomes darker. I tried smc reset. pram reset doesn't work because i can't get computer to boot for keyboard to be recognized I switched ram modules, no difference and tested each memory port. How do I know if this is a cpu or gpu problem?