Constant reboot after 1 sec into W7 splash screen

Setup
Motherboard: ASUS M5A99X EVO
Processor: AMD FX 8120
Cooling: Corsair Hydro H100
Memory: 3x Crucial DDR3 2GB sticks
Graphics Card: Sapphire HD Radeon 7870
PSU: AXP 1000W Gaming series
Chassi: CM Storm Trooper


As the thread-titel claims, my computer reboots everytime I attempt to boot.
I've got 2 individual HDDs, one with W7 ultimate 32-bit and the other with the 64-bit equivelant.
Either of which have the same issue. I get to the point where the 4 colours of the flag allign, just to see my system reboot completely everytime.
It's a new system.

The drives work fine, and boot just as they're meant to on my previous system. But on the new system they freeze and reboot at the exact same point.
When I try going into safe mode on either, the list of files required loads up, but then instantaneously reboot again, without actually letting me into safemode.

Thanks in advance for replies.