What happens if you plug both the hard drive and the short CD drive from the tower in your desktop? If that works you can be pretty sure it's the drive that's causing troubles. I recall having the same problem before swapping my Seagate with a 4GB IBM.
Ehr.... Hold on a minute... You say the Tower has a Quantum Atlas... That's a SCSI drive! Not IDE! Sure it's not a Quantum Fireball?
