Gigabyte motherboard won't POST, phase LEDs all on

Hello,

I've had my PC nearly a year and it suddenly decided to stop booting. It just sits there, with the phase LEDs all on, and doesn't beep or display any video output. There are four lights displaying green and yellow next to the RAM slots, I think they're the DDR voltage. Also, the lights on the mouse and keyboard never come on.

I've unplugged everything and breadboarded the motherboard, the only things connected are the CPU/HSF and PSU. Also, there are no memory warning beeps with the RAM removed (and before you ask, yes, the speaker's attached  

These are my specs:
* Gigabyte X58A-UD3R
* i7-930
* Scythe Mugen 2 Rev B
* Corsair HX1000W PSU
* Corsair XMS3 1333MHz 7-7-7-20 6GB
* inno3d GTX480
* Case: Coolermaster CM690 ii advanced

The CPU was (moderately) overclocked but I reset the CMOS.
Is it worth getting a multimeter to test the PSU? I find it hard to believe that such a powerful PSU would fail, especially one that got such good reviews.

Any advice would be greatly appreciated.