Don't know if you tried this, but try booting back into OS-X and make sure the keyboard works. (Is it plugged in ok? Dumb question, but you never know)

If you can operate it from OS-X then uninstall and re-install windows. A pain I know, but that's all I've got...

Well, you can get into XP right, look at device manager and see if the keyboard is even recognized. You may have to change the parms for the keyboard while in XP.