Recently I was upgrading my Linux distribution (specifically, fedora, but I've had this happen on Ubuntu & Debian), and ran into a weird problem where parts of my keyboard weren't working. I've got a Corsair keyboard, and I've had this happen a couple of times.
It turns out that once in awhile, for whatever reason, the keyboard needs it's own reset. While I haven't narrowed down the culprit, the fix is relevatively easy: