I'm at a bit of a loss as to the problem with my PC now. Very confusing.
I had a GA-P35-DS3 motherboard, with a 500w PSU in it and a 8800GTS video card. And the CPU was a Q9300.
One morning, suddenly I have no video output at all. A few reboots, nothing (not even a POST or BIOS screen)
However... I could Remote Desktop to it (even through LogMeIn, or even VNC) All of those worked fine. So once using VNC, I checked out the Nvidia Control Panel and Device Manager, both of which tell me there is no VGA card reported present.
At this point, I'm sure its my VGA card. But being paranoid, I take it to my office and my colleague tests it on his rig... it worked perfectly. Nothing wrong with the VGA card.
Only one option... it MUST be the motherboard!
I purchased a Gigabyte Z68XP-UD3, an i5 and have just finished rebuilding it. I've got the 8800 GTS in there too.... no video output!!!!!!
Still no video output!!!!!
As the VGA card works in my colleagues rig, I've ruled that out as being the problem. I'm at a loss... what else could be wrong?
After all that, I'd guess the power supply is not providing enough to the GPU. Ordinarily, I would've guessed the GPU and then the motherboard slot, but you've most likely ruled both those out by testing them in other systems. The PSU is the only thing out of the components you've mentioned that's stayed constant and still caused a failure.
If you have a friend who lets you try your GPU in his machine, ask if you can try his PSU in yours instead. I swear it's not as gay as it sounds.
Aside from the PSU potentially being bad, have you verified your monitor works on another machine? Also, if your monitor has multiple outputs, have you tried changing the source? Sounds silly, but maybe we're over complicating things here.