Also, trying to connect the keyboard to a different USB port and/or without an USB hub inbetween can help. I had that problem on my Linux desktop before (finally) replacing the motherboard.

On Windows, starting all the way back on Vista, you can also use the on-screen keyboard to log in if the mouse is still working. At least according to https://support.avast.com/en-ww/article/windows-on-screen-keyboard/#pc. With a long, secure password this isn't quick, but it's enough to be able to access Windows and start diagnosing the problem.