Your computer for some reason reset the USB hardware stack You should still get generic keyboard functionality at least from the built in windows drivers unless you have a bluetooth keyboard of some sort.
To get around it temporarily, find an old PS/2 keyboard, one of the ones with the old non USB purple round connector thingy. Plug that in, should let you in far enough to investigate further or at least access bios.
If something took out your operating system to the point where it dumped all your hardware configuration and can't find them from the default system files, You may have other problems, Destabilized operating system, Hardware overheating, Hard drive bad sectors, Virus, etc. I don't really know without alot more specification information. Event log should have some information in it as well.
Were there any recent blue screen errors or hard power offs?