|OK, look, let's stop making assumptions. Assume something the WORST, like maybe there's a chunck 'o left over metal that finally fell down and shorted something.|
SO REMOVE THE MOTHERBOARD FROM THE CASE.
STRIP EVERYTHING and lay out the motherboard and power supply on a "safe" table and hook up ONLY this:
The motherboard, with RAM and CPU
Keyboard and power supply
Video card, if separate, and monitor.
THAT'S ALL, nothing else, and now see if you can get post, and a "bios" screen.
(Pay attention to beeps, and note them)
If possible, try a different video card, and known good monitor.
Try resetting (clearing) the bios. If you don't have the manual for the board, just pull out the battery (with the power off) for about 1/2 hour, and reinstall the battery
If possible, pull out one RAM stick, if more than one, and try different slots.
You might just remove the CPU and reseat it in it's socket.
Try a known good power supply.
AT THIS POINT if nothing works, you either have a bad motherboard, a bad CPU, or bad RAM, or even a combination of those.