The first step would just to be to examine all the molex connectors on CPU board. Any wires popping out?
Next would be to look at the switch matrix. If all of row five is out you should be looking for the You should be able to look at the matrix diagram (attached). According to that, row five is a green-white wire. Follow that everywhere it goes and look for breaks, shorts, etc. Make sure there is continuity going into the CPU board.
If that doesn't fix it then you've probably got something else going on. I have a TAF that when I bought it, there was extensive damage to the CPU board due to the batteries leaking. This ended up destroying quite a few traces on the board. Fixing them was easy, it was going through the board trace by trace that was the tedious part. Once they were found, I just re ran the traces with 30 gauge wire.