I know hdd data recovery is not cheap. However, my photographer brother, had his external maxtor(I told him not to buy it) die, while in the process of backing it up. The drive shows on disk management now as unallocated. Who can get his data(photos) back relatively inexpensively, but reliably. Assuming the two are not mutually exclusive. The drive shows as unallocated on two other computers.
Try connecting the drive to another computer. It happens to me also.
The trick is to connect it to another computer and then everything is fine.
If you need data recovery programs, I recommend Spinrite or GetDataBack or similar.