Strange that.. I would have gone straight to the floppy drive. Like check the ribbon, check the power, make sure there isn't a pin pushed in or the ribbon was the wrong way round. Sounds like you have something backwards thats all. Have you also taken the motherboard out of the computer and ran it safely not in the casing... Maybe even disable the floppy drive and attach an external only... Maybe just shorting somewhere... Did you disable the floppy drive and try it.... and I mean take the floppy drive out the machine. Also check wires to keyboard that they are not cut... sometimes happens from the shielding. Dunno.
