My Computer isn't Booting When it's On. Help Please!

My computer no longer boots up when I turn it on. It started yesterday when I was installing more fans in preparation for an upgrade. At one point I took the 2-pin jumper off the 3-pin CMOS switch, and it powered on fine, but on the next power up it no longer booted. The blue-LED fans still run fine as well as all the other fans such as the graphics card, but the monitor doesn't register with the computer at all.

I highly doubt the graphics card is to blame since the keyboard and mouse aren't lighting up blue as they should be. On top of that, I switched out to a new motherboard today and still had the same problem. So that leaves either the power supply, cpu, or ram (and maybe the graphics card, but I honestly don't see how). If it were the power supply, my computer might not be turning on at all.

I get two new graphics cards in tomorrow as well as a new power supply, so if it still doesn't work it will be narrowed down to the cpu and ram.

Any help and suggestions are appreciated. I don't know what to do.

[EDIT] I also tested with the RAM today to see if any of it was faulty and if my computer would run on any of the three sticks, but it didn't work.

EDIT With system specs:

CPU: 2.13 ghz duo core

RAM: 3 x 1 gig of ddr2

PSU: 500 watt

Graphics Card: 7950 GT

So it doesnt boot, I think it might be the psu. What is the brand of the psu?