Have you tried accessing this drive from another computer?
At this point I must get on my soapbox....
[soapbox on]
External drives (USB, Floppy, etc.) are significantly less reliable than internal drives. I can't count how many times I have had to try to rescue someone's data from an external disk, drive, etc. In my opinion external drives should be used as backup devices not primary storage devices. If it is used as a primary storage device then it needs to be backed up just like internal drives do.
[/soapbox off]
Sorry for the mini rant, but it really surprises me how many times I have seen a situation similar to this......