MacBook Pro Keyboard – Fixing Apple Wired Keyboard Not Working

Did you have a Logitech keyboard at one time? If so, you might have an old Logitech kernel extension that is causing problems. Uninstall the Logitech control panel from System Preferences and look in /System/Library/Extensions and delete LogitechHIDDevices.kext and LogitechUnifying.kext (reboot for extra certainty). Many people have had problems due to the Logitech stuff on Mountain Lion.

If that's not it, your problem still could be caused by something similar. Third-party kernel extensions are transferred during a system migration. Likewise it could be a more run-of-the-mill extension conflict.

You should try using the keyboard extension cable that comes with your keyboard. For somewhat obscure reasons, this solved the problem for me and other people trying to use the Apple Wired Keyboard with USB hubs. See also https://apple.stackexchange.com/a/179299/33925