specs on bottom

About two weeks ago an error about USB over current started to appear upon post, where the computer would shut off automatically after 15 sec. I then unplugged every USB device connected, as well as the internal front USB connection. This did not help. After 5 maybe 6 attempts to boot the bios wouldn't even post. Today all that happens is that the CPU_LED lights up and nothing else... I can't even turn the computer off by holding the power button. I have tried to change PSU, used only one RAM stick in every RAM slot, change Video card and PCI slots, reseated the CPU with cooler, and even used a multimeter to check for shorts on the on-board USB connections as well as a visual inspection to see if there was any damage or debris...

nothing... could it be a faulty bios chip, or a shorted or faulty USB controller on-board?

This was totally unexpected since the motherboard has worked flawlessly in operation for about 4 years...

hope you could help me shine some light on this problem.

MB: ASUS CROSSHAIR V FORMULA
CPU: AMD 8150-FX
GPU: 2x XFX 7970 CF
PSU: XFX 850W-BLACK EDITION
RAM: CORSAIR VENGEANCE-LP 4x4Gb
SSD: SAMSUNG 840EVO