I had some of the lower row of keys go out on mine and it turned out to be the ribbon cable had developed a crack in one of the traces. If you look, the cable is actually folded pretty tight and from all my modding, I'm sure I flexed it one too many times. I was lucky and found that when I pressed it against the base of the keyboard it worked, so I got out the superglue and actually glued the cable to the metal bracket to keep it from flexing. Works fine (so far).
So, try this, unscrew the keyboard and lift it up but leave it plugged in. Try flexing the cable while pressing keys and see what happens. If the ribbon is bad, best to just order a new keyboard.