I know this sounds stupid, but it ,ay be hardware, so I have to ask. are you sure that it's not hardware? Check to make sure that the drives aren't both trying to be master or slave, if that's not the problem, try switching the master and slave.
I just mention this because after years of doing hard ware shit, I was having similar problems and it turned out that both drives were set to master. At which point there was much self-abuse.