I connected my 1TB USB HD to a server for backup purposes. After a week or so, it disappeared and not appearing back in My Computers or Device Manager or anywhere. I connected with another PC and it comes up fine, any solution to that?
You did not mention what OS you're using, what kind of external casing its about, whether it has its own power source or not, what kind of error messages you may or may not have had, whether you tested the drive on the other computer, whether you tried multiple USB ports on the server, etc.
Without providing more data, your question is not answerable.