Wanted to thank you guys for your help. Went back to a system restore point from a few weeks ago, and that helped but didn't fix the problem. Turned off the auto-reboot per Spanks suggestion and figured out it was my wireless PCI card driver causing the problems.

Who knows why these things go bad, I haven't changed anything on this PC in a while. I reinstalled the driver, then updated it, to no avail. Ended up finding a driver for another similar product, which seems to be working great. Thanks again everyone!