For PC's only-
1. Boot clean. ( F5 or F8 at beep )- get to a Dos prompt.
2. Run "Guest" from floppy.
If it double clicks, wont spin up, or still cant find it, it's a hardware problem (bad connection or drive) (( if scsi- assuming you have correct Dos scsi driver active)).
If it does find it- it shows something in Windows is interfering- (like a printer driver).
Delete a few drivers or tsr's until you find it.
--- or -- pay a few bucks, call tech support, and have them tell you the same thing.
If it's a bad drive- you'll have to call anyway to return it and get it fixed.