Hmm, too many variables to troubleshoot.
First have a look at this old post, it just may have your answer:
I'm thinking perhaps there is a conflict in relation to IDE/SATA and/or Single Laser, etc. Then again perhaps a ribbon has been damaged, etc.
Have a check with that thread and let me know if you can work anything out because to be honest there really is a lot of possibilities to the cause at this moment. We need to dig deep!