Crashing Phenom II X3, Help

Friend built a brand new PC, specs as follows:
Mobo: ASUS M4A79T Deluxe
CPU: AMD Phenom II X3 720
RAM: G.Skill Ripjaw DDR3-1600
GPU: Radeon 5770
PSU: SeaSonic S12E Bronze 650W

We tested the RAM with gold mem or memtest (can't remember which) and it passes 12 hours, we tested his HDD with no errors, video card runs benches with no problems, we tested his CPU in my board, no errors, PSU runs fine on a PSU tester, voltages are good.

So we thought the board had problems. One RMA later and it's still freezing/rebooting occasionally.

Ideas?

proper standoffs? remove any extra USB stuff (front panel etc) since sometimes they arent always wired good.. try booting the bare minimums?

Will do that and report back.
Forgot to mention
OS: Windows 7 Pro (retail version)

Is it 64 or 32 bit (just wondering...) and have you tried other OS's?
Was it a clean install, with all the latest motherboard drivers?
Have you tried flashing the BIOS to the latest version?
If you have the latest version, have you tried a slightly older BIOS version?
Are you running stock everything (as in not set to auto in BIOS; including: ram speed, system bus, cpu multiplier, cpu voltage, HT multiplier, northbridge voltage, ram voltage, ram timings.)?

It is possible to receive 2 bad boards one after the other, although rare.

I'd think it is the RAM voltage setting - I know on my Gigabyte MOBO with DDR3 1800 2.0V Ram it would auto set the RAM as DDR3 1333 @ 1.5V on the initial install which made it unstable in windows due to the low voltage until I manually set it in the BIOS.

Is the HDD SATA? It may be strange, but have you tried using different SATA cable? I've had a similar problem once and it also happened on a friend's machine, switched cable and everything was good after.