Sister has windows 2000 Pro . The PC starts up and will run but the keyboard will not work. It reads "error 31 " .This keyboard was working fine.The mouse works.She ran Norton Sys.They say it worked after system check .I don't know what they did after the check or removed . The keyboard is : Fellows # KB 2971 - Part # 99148

Have you tried another keyboard?

Borrow another keyboard for trouble shooting purposes. It doesn't have to be the same brand but the plug on the end of the cable must be identical. Plug the new keyboard in with the PC turned off. When the PC is powered on, Windows 2000 will recognize new hardware & reconfigure itself, if necessary, to match the new hardware. If a new keyboard is the answer, a generic keyboard is very inexpensive these days.
If the "borrowed" keyboard does not resolve the problem, try a different port. If that keyboard is the older PC2 type (recognized by the round plug), try a USB keyboard in any available USB port.

When you plug the keyboard into another computer, does it work?

Assuming the keyboard is working the most likely issue if it's a PS2 keyboard is that the PS2 port has gone bad, either try a USB keyboard or get a PS2/USB converter for the keyboard. Also good info for us to know is does the keyboard work before it gets to windows, in other words can you get into your BIOS or to the windows boot selection menu(F6 for that after boot test) or during boot test for bios depending on mother board F2-F12(F2, F4, and F8 are most common) if your keyboard is working pre windows then it's a driver issue and I would suggest just using a different keyboard.

If your keyboard is working pre windows and a new keyboard still isn't working in windows a system file may be corrupt, so first I would try to repair windows and or getting the appropriate system files from a working PC and replacing them.

Hope that helps.