Hi there Sherlocksh,
Unfortunately, it is possible that the enclosure or the HDD itself has failed.
One thing you can try is to attach it with a different cable to a different port. In case the issue persists, you can try to access it with some data recovery tool:
http://www.tomshardware.co.uk/forum/id-1644496/lost-data-recovery.html
If the drive can't be picked up by software tools, you can:
- RMA the drive if it is under warranty.
- Contact a data recovery company in case the data stored on the drive is crucial.
- Some users take the drive out of the enclosure in order to connect it internally. Keep in mind that this will void the warranty and may not work in case the drive has proprietary connectors.
Let me know in case you have some more questions,
D_Know_WD