My computer has lost its SOUL!! :(

hi all,
I have this computer, a custom build, which has been soldiering on for just over a year. Just yesterday this problem arose, where the computer suddenly BSODed while I was running a non-intensive program. That day the computer had already been annoying me, with very slow performance and crashes (had to restart 5 times that day!)
So yeah, now it was not booting up!!. When turning the computer on, all lights and fans in the case would turn on but NO DISPLAY (just a black emptiness) would come up on the monitor (the power is fine, as the light at the bottom right of monitor is on). during this time, (about 9/10 of the time, I can hear a fan slowly getting faster and faster until it reaches what sounds normal.)

There has only been ONE "fix" to this so far, where I switch off everything from the wall for up to an hour. This normally ensures the computer boots up, although at some point it just freezes/crashes/BSODs. In this game which normally runs at nice FPS (40-50), the max I can get is 36, although average is 26, which is VERY noticable.

From what I've gathered, it could be a problem with my RAM, CPU, motherboard, a cable, or the videocard. It could also be a some problem where things are shorting. I'm soon going to remove some things, clean them, and then place them back in. I have a feeling something is shorting

My hardware:
q9550 (core 2 quad)
HD 4870X2
P5Q C (775, intel)
4Gbs of DDR2 1066MHz RAM (2 sticks)
800W PSU

NOTE: The processor has been OCed to 3.5GHz for several months now, on STOCK voltages. During the problem, I managed to get into BIOS and tune down the OC a little, with no results.

Thankyou for your answers! (if you've read this far xD)