Gigabyte UD3R loops at POST

Try clearing CMOS manually. And put RAM voltage to 2.0v and see. Also see if the battery is dead. Dead battery can some times cause this. Also what PSU? If it's a no name PSU that could/may be a reason.

My UD3R does this periodically at boot up and I just turn the thing off at the PSU and wait a few seconds, turning it back on and booting up normally.

This is very similar to the Asus cold-boot issue that I had on a P4PE a while ago where it would just not start at all until I shut off the power at the PSU and turn it back on at the PSU.

Why this happens seems to be manufacturer specific. Each one has a different quirk and the Gigabyte's is the looping post.

There are plenty of disparate configurations out there and many people experience it with the common denominator being the Gigabyte boards.

Try the power switch on the PSU and restarting. If that works, you just have to do this now and then like I do.

By the way, my configuration is entirely stock with name brand components and no overclocking.

That's my point of view anyway.