Here is a problem that is as silly as it is frustrating. I'd be curious to know if anyone else has experienced this.
I have two computers- one Linux and one Windows, and use a switch box to share the mouse, keyboard, and monitor.
If I switch from the Linux box to the Windows box, and then back to Linux, the keyboard and mouse no longer respond. The Windows machine is fine.
I thought it might have been a hardware issue, so I booted the Linux box to Windows, and then switched between the two machines. The problem only occurs with Linux.