WD 500GB HDD

If it's [b]IMPORTANT[/b] pack up the drive and send it to a Data Recovery Specialist and pay them to recover your Data.

If you mess with the Drive unsuccessfully the cost of a Professional Recovery is going to be much greater and the chances of a 100% Recovery greatly reduced.

However if it would just be [b]Nice[/b] to recover your Data and you can afford to loose it all you can try plugging the drive into a running computer and running [i]chkdsk /r[/i] on it from the command Line in Windows. Sorry but there is no GUI for this you need to use the Command Line.

Or you could try one of the many Data Recovery Applications available you can find a short list here for them if you want to attempt this. ;)

https://www.techrepublic.com/forum/questions/101-342724?tag=content;discussion-table

Apps you can try

Spinrite 6.0 (www.grc.com)
undelete
and a ton of others.

Many times the problem is not the hard drive in the enclosure, but the enclosure itself.
You are not going to be able to use it as an external anymore so remove the drive from the housing and plug the drive directly into your PC. Many times the drive is fine.

Note: External drives are for BACKUP not primary storage. You should have all data in TWO places not just one. If you did you would not be in this predicament. (Lecture Over)

Good Luck