I had multiple customers calling me this week when suddenly their keyboard stopped working.
Everything was working fine, they rebooted their computer, and after the reboot their keyboard would no longer work. Even if they tried different USB ports or different keyboards, still no luck.
After chasing my tail for a couple days, I was finally able to figure out the root cause of the problem.
A couple of years ago I had installed Hitman Pro Alert as a measure of protection against Cryptolocker.
For some reason, after two years, it is now preventing users from being able to use their keyboards.
All you need to do is uninstall the software and everything will be back to normal.
For those who have remote access, you can login remotely and uninstall it.
For those with only local access, you can login to safe mode and do it.
Hopefully this helps someone!