PC POSTS, will not boot windows

ASUS A8N SLI-Premium
AMD Athlon 64
400G hardrive
2G ram
Raedon HD4890
700W Kingswin PSU

Rig is about 4 years old now, I just added the PSU and video card about a month ago.

I woke up three days ago with the Mobo beeping every couple of minutes. Initially, thought it was the smoke alarm, but it seems like the computer was just rebooting itself in an infinite loop...

I can turn it on, POST completes without a problem, then I get the "Windows did not successfully shutdown...." with the typical options, boot in safe mode, safe mode with networking, safe mode with command prompt, last known good config, or boot normally. No matter what option is selected, the Windows splash screen appears for half a second, and then the system just restarts itself.

What I've tried so far:
Clearing CMOS
Removing mobo battery
Removing non-essential components
Removing USB peripherals/devices

I assume my next step is to boot from a CD and reformat the hard drive. However, seeing as how I'm at college and don't have a handy windows CD, I figured I would ask if there was anything I could do in the mean time...

Any help is appreciated.