2007 macbook pro won't boot. What's the easiest way to diagnose the problem? My 2007 Macbook Pro Santa Rosa just developed a problem where it failed to wake from sleep. I power cycled it, and it would not POST. I removed the battery and discharged the capacitors by holding down the power button, but laptop will not POST. The front light on the unit's latch powers on (steady light), there is a noise from the DVD drive as if it's checking for the presence of a disc, and a small amount of hard drive activity, but the display remains off.

It's been sitting on my desk for months. There's been no physical or liquid damage to it. I did notice prior to this that the DVD drive would occasionally check for DVD's for no reason (unit was sleeping, suddenly the DVD drive starts making noise), but I figured that had something to do with installing Mountain Lion about 2 months ago, since that's when I started noticing that issue.

What's the best way for me to diagnose the problem (motherboard, power supply, or something else)? I doubt it's worth getting it repaired by Apple, given the age of the unit, but if I can figure out what's broken I might swap out the offending part.
The mid 2007 MacBook Pros (MBPro 3,1) and the early 2008 models had defective NVidia GPUs that would cause failures similar to yours. The GPUs would fail at various times (6 months in for some, 3-4 years later for others). When that happened, Apple fixed them without charge.

If your MBPro still has its original NVidia GPU, then the problem could very well be that. Unfortunately, Apple's repair extension program for this program ended on Dec 7, 2012.

You might be able to find a replacement logic board on eBay or Craigslist.