P6T Deluxe V2 will not POST, keyboard gets no power

I recently had a hard freeze while playing Crysis 2. I had just increased my video card OC by about 5% to squeeze a few more frames out (I had just downloaded the DX11 ultra high-res patch for C2).

After manually restarting, PC would not POST. I tried all the tried and true methods: resetting CMOS, removing CMOS battery, switching off/unplugging PSU, unplugging all components and power, reseating video card, and using just one stick of RAM.

So far my only results are two successful boots of the ASUS splash screen. The first time I was able to press Delete and attempt to enter the BIOS, but I was left at a black screen with a flashing cursor. The second time my keyboard was not powered up, so I could not attempt to enter BIOS.

I have booted dozens of times and only got to the splash screen twice. Both times it was with all minor components unplugged and one stick of RAM in the first orange slot. Other than the one time I cannot get keyboard or mouse power from any USB slot (I have tried all 6 on the back and 2 on the front).

I am confused because this could be many issues, namely PSU, mobo or video card. I am starting to suspect PSU. One other note of information, I have plugged in an internal speaker and do not hear any beeps if no RAM is inserted. Here's hoping my mobo is good...

Any ideas would be greatly appreciated. Thanks.

specs:
Asus P6T Deluxe V2
Intel i7 920 @ 4.0GHz (previously)
2x3GB OCZ Platinum DDR3 1866 PC15000
Sapphire Radeon HD5850 @ 875/1250 (previously)
Corsair 750TX