At least you can test the unit in several ways to narrow down the fault
1.Try it plugged into a friend's computer. If the OS is 2000 or XP it will configure itself.
2. Open the case, remove the drive and hang it somehow as an extra drive in your PC. To avoid jumper troubles "borrow" the data and power cables from the secondary master, (probably an optical drive)you should be able to read it.
When I said "hang" it, I mean that almost literally.
For test purposes there is no need to screw anything down. The drive can be on the table or almost dangling from the box just as long as it is not knocked during the time it is switched on.
If you can read it then obviously the fault is in the external case, HDs alone tend to have very long lives.