There are three possible outcomes:
1) The external drive circuitry is damaged
2) The internal hard disk is damaged
3) Both the external circuitry as well as the disk is damaged.
Disassemble the unit and take the hard disk out. Connect the hard disk to another external enclosure and try to run it. OR - Connect the hard disk as an internal disk in a computer and try to run it.
If all of the above fail and the data is valuable, take the disk to a data recovery service. Expensive!
Frequent backups of all HDDs are highly recommended!