Having had the same thing happen to my external drive a few months ago I'll echo the suggestions to get a new drive. In my case it appeared that the problem may have been a corrupt file registry but I wasted a few days trying unsuccessfully to repair it. Tripping on a lead and dumping the drive on to the floor finally put paid to any other fixing attempts.
If the stored files are really important to you don't rely on a single backup either. Burn CD/DVDs of them too.

I don't know for sure, more knowledgable people here will, but I think that having multiple partitions on the external drive may, in some cases, lessen the chance of loosing all files in one go.