I had the same problem with my number keys, the Num pad still worked, but + and - and of course Equals and Underscore, went out. I borrowed a cheap Keyboard, and then remapped the bad keys to my Nostromo 52 speed pad. Made a new profile for it and voila, I had functionality back.
IF you have an alternate Device, that you could remap the function keys to, you might try that. Or as Nem says, try any other Keyboard, and see if the Function keys works on it.
Stephen