Hi there Disgruntled Amoeba,
There are two options:
- The enclosure or the cables got damaged. In this case, I would advise you to start with trying different cables. If the issue persists, you will need to take the drive out of the enclosure and connect it internally through SATA in order to retrieve your data. If you manage to do that, then you can just get some third party enclosure, put the drive back in and use it as an external one. Just make sure that the drive is not hardware encrypted.
- The HDD is damaged. If the drive is not recognized even when connected internally, then most probably there is something with the HDD itself. In this case, you will need to contact a data recovery company.
Hope this will help,
D_Know_WD