Why would windows not see my keyboard?

This is weird, one day everything is working fine, the next day I come home and my keyboard isn't working. Well, I unplugged/replugged, tried different USB ports, etc. The strange part, though, is that the keyboard is not work only in windows. When the computer starts I can still access the BIOS and and can get the boot options by pressing F8, so they keyboard itself is not broken, but when I get to the login screen on windows, my keyboard won't function!
Any idea what could be causing this? I wanted to do a system restore but for some reason it seems all my restore points were erased =/

Possibe virus sproblem.

While a virus problem could occur, this sounds to me more like a driver problem, as Mike mentions, or perhaps a general corruption in the OS. As Mike suggested try a PS/2 keyboard and see if that helps. At the same time, since the "restore points were erased" I'd lean more toward a corruption in the OS. If possible, you might try doing a repair of the OS with the installation disk, if a PS/2 type keyboard doesn't work.