Keyboard not working in Boot Camp partition

I've been using my Windows(XP) Boot Camp partition for many years without any issues. But now when I boot my Windows partition the keyboard is not responding, thus I cannot enter my Windows password. The mouse is responding OK. And the keyboard is also working fine in my MacOS partition.

This is the first time I boot my Windows partition since I upgraded from Yosemite to Sierra a couple of weeks ago. So I strongly suspect this has to do with it, but I have no idea if or how it can be fixed.

Any suggestions?