Well thanks for that compliment, I would start going through that drive and get rid of everything you don`t need or can`t remember what it is. Try to start moving the files back onto the original machine if you have the room. If you manage to get it empty, try to format it and see what happens.
Make folders on the external and dump the files into them, documents, pictures, etc. that way it`s much easier to move them. After you copy and paste them, verify they are good, then delete them off the external.