I have a Toshiba Satellite C855 where both Ctrl keys simply quit. Here's what I've tried so far.
I tried pressing Ctrl + Alt + Fn (Numerous websites suggested this for a Toshiba machine.)
I tried re-installing the keyboard drivers (by uninstalling the driver in the Device Manager and rebooting).
I tried rebooting in Safe Mode to determine if a particular app was causing the problem.
None of these steps fixed the issue.