I have 2012 MacBook. Shift and Alt keys not working. Tried everything, even installing OS from scratch.[br]
As I have two hard drives on it, seeing iOS applications etc on both of them made me think that something might be conflicting there. First I erased everything on the second drive, including hidden files and formatted it after all. Three restarts, the keys are still working, fingers crossed it stays this way. I hope it works for those searching for the tips as it did for me.