The PS/2 keyboard on one of my HP laptops suddenly stopped working, for no apparent reason.
Checking control panel indicated the keyboard "was working properly", but of course, it was not.
Perplexing . . .
Then I searched here, found an entry from a few years ago that suggested powering down, completely unplugging the power supply, AND removing battery for a few minutes.
Have no idea why this works, but, amazingly, put the battery back in, powered up, and the keyboard now works perfectly!
Maybe this is something lurking about in the BIOS (just a guess on my part), but this really does work.