New System Won't Boot Anymore

Recently replaced the mother board on my new build to the B3 Rev. System had been working fine (2 weeks regular use) until tonight when I switched it on and it all booted fine, I used it for a couple of hours no problems, went away for 30 mins came back and it appeared like it was off? Definitely wasn't asleep, but power light on the case was on (strange), 1st so I hit reset button which did nothing, then tried power button on case which did nothing. Turned it off at the PSU, then back on a hit power, and the system boots, fans come on, hard drive spins... then nothing? It doesn't switch off, the fans keep running but no post. No beeps either (usually get 1)

CPU has been OC'ed to 4.3ghz and was stable temps around 60c at 100% load (ran Prime95 for 1.5 hours)

Any help greatly appreciated.

Full system specs:

Asus p8p67 Pro MOBO b# Rev
i7 2600K CPU
Cooler Master Hyper 212+
Gigabyte gtx580 GPU
Samsung 1TB F3 Spinpoint HD
Sony DVD RW
4 GB Kit Corsair XMS3 DDR3 1600
Antec TP750 PSU
Windows 7 64 Home Premium
Coolermaster 690 II Adv

I would check your connections on the inside to make sure they are still stable. Could be a loose connection maybe.

Back up and running

Did a partial rebuild (Reconnected all plugs to MOBO) reseated RAM and GPU. Cleared CMOS while I was at it and away we go. Might see how it goes on factory settings for a while. The ASUS UEFI appears to behave strangely... parts of the interface disappearing, settings not saving properly etc.