My keyboard stopped repeating - how to fix?
Well it looks like there are a couple solutions:

Option 1. Enter this in terminal: defaults write -g ApplePressAndHoldEnabled -bool false. To disable repeating keys again, enter the same command except change the false to true.

Option 2. Download Mountain Tweaks (I assume you're on Mountain Lion, if not, download Lion Tweaks) and click the "Yes" option for "Enable Repeating Keys":