Not Joking, just tired from arguing with the computer...yeah, the cable on the A4000D to which the CD drive is attached is, in fact, the cable to which the HD is also attached. I don't know why I couldn't see that mistake while I was checking for spelling...but what the heck. You get the idea. However, the point of the problem is that both drives work on the tower and only the long cased drive works on the desktop model. Both claim to be eide....makes sense since both work on the tower. Both are set to "slave". Each computer can get at least one drive to work, but the issue is why the shorter cased drive, the one which would actually fit inside the desktop case, will not run on the desktop? Idefix is not much of an issue, I would have thought, since the longer drive will run when hooked up to the desktop model. The operating system on that machine knows how to make a CD drive work...but not, apparently, if it is in a short case. So aside from the length of the drive, can you think of anything else that might make a difference?