Not booting. Flashing power lights.

That is a very good question. I ran into a similar problem with an ASUS laptop and oddly enough removing the hard drive allowed the system to post video. The laptop was brand new so I decided to send it in for warranty service. When I got it back, ASUS declared the problem was the motherboard and had replaced it before sending it back to me. I know that that kind of solution is not a good one for you, but the best steps to take are to remove the hard drive, cd drive, wireless card, and modem card (if applicable) to see if any are preventing the system from being able to operate properly. Each are important to remove as I have experienced situations where they have prevented me from being able to properly use the computer. Finally, if all else fails, remove the RAM from the system and listen for a beep code. If you do not hear any beeps then the motherboard is the likely culprit, else, it could be your CPU (either case is never fun).