Reboot loop is driving me nuts

I can't think of anywhere else to put this, since Ubuntu is working on the machine. I have Windows 7 SP1 installed on my custom built pc, but I can't get it to boot, and it's baffling.

I've got the following specs:

Intel i5 2500k (not overclocked)
Gigabyte GA-Z68A-D3H-B3 rev 1.0 (Bios F10)
Currently: 4GB GSKILL Sniper DDR3-1600 9 9 9 24 (used to have 8GB, but one stick apparently crapped out on me this week).
500GB SATA HDD
I'm currently using the onboard video for troubleshooting purposes.

Last week, I got my first BSOD on this build, soon after installing DX10 and 11 for some steam games (I'd used the computer with no problems for over a month). I couldn't get any display with my old 8800GT, so I reset CMOS and removed the 8800GT, and got video back in time to see that it's stuck in an endless reboot loop.

I've tried loading fail-safe defaults, optimal settings, and just about everything I can think of in the BIOS settings. I've tried repairing the master boot record, but no luck. It boots past the BIOS screen, then displays "Loading Operating System" for about 2 seconds, after which the screen goes black and the system reboots.

I can't boot into safe mode (I can't even get the options for safe mode), and I've even tried reinstalling Windows 7--it made it through the installation with no problems, and had no problems until I told it to restart. Then it did the exact same thing it was doing before--reboot loop at the "Loading Operating System" screen.

I've installed Ubuntu onto it and have zero problems running Ubuntu--all peripherals and devices work without issue. But when I select Windows 7 in the boot selector screen at the startup of Ubuntu, it does the same thing--reboot loop.

I've disconnected the reset switch, reseated all cables, tested the memory, and done just about every basic troubleshooting I've found online. Does anybody have any idea what could be wrong? I really appreciate your help!