Computer boots up twice

[iamapizza]

I've got a weird problem - when I start my machine up, it turns on for a second, turns off, then turns on again and then gets to the POST check. After that, everything is fine. I can stress test, play games, everything just fine. It's just that weird first boot. I believe this only happens when overclocking it, I don't recall this ever happening when I was running on stock speeds. Any clues or steps I could take to get rid of that first boot?

I've uploaded a video to show what's happening:

http://tinypic.com/r/1o3prr/7


The setup is:
Motherboard: Asus P67 Sabertooth
Processor: Intel i7 2600K @ 4429.7 MHz
RAM: G.Skill RipJawsX 2x4GB DDR3 PC3-12800C8 1600MHz
Cooling: Corsair Hydro H60
PSU: Corsair AX850W
Graphics: EVGA GTX 580 (normal 1.5GB, not overclocked)

I had a TX650W PSU until a few days ago and an AX850W now, swapping PSUs has not made a difference.

 

[mcnumpty23]

this happens quite a lot with asus boards for some reason --my p5k used to do it as well but only when it was overclocked--i just got used to it in the end up