New comp turns off to reboot, sometimes reboots during boot

I just got a new Sandy Bridge Motherboard/CPU with new DDR3 RAM. It's currently running through the latest Memtest beta build. (Tip for any other sandy bridge adopters running Memtest: Anything but the latest version will hang. It's not because your new build is bad, it's just incompatibility. So before you freak out, make sure you have the very latest beta from here - there's an .iso too if you scroll down.) All seems well on the memtest front so far.

However, I've already noticed some strange behavior regarding booting and rebooting. First, when I press the reset button, it seems to power off entirely - fans stop spinning, LEDs turn off - for a good second or so before turning back on. Perhaps this is normal for the particular board, but I can't recall having another computer that responded to the reset button like this.

More worrying is that sometimes, when it then reboots, it will sometimes do this again - shutting down for a second or two and then booting back up - after the Gigabyte boot-up screen appears. This has me worried I have a faulty board (or faulty/inadequate power supply).

Specs:
Gigabyte P67A-UD3 motherboard
Core i5 2500k
8 gigs RAM (2 x 4GB Mushkin 991770)
Corsair VX 550 watt power supply
Radeon HD 4770

I haven't touched any overclocking options. The power supply and Radeon are from my prior computer and worked fine there. I suppose that doesn't get the power supply entirely off the hook as it was a lighter motherboard & CPU, so perhaps the extra power draw is making a difference.