Hi there aunnoman,
Unfortunately, you HDD could be failing.
How is the drive recognized by Disk Management?
You can start with just using a different USB cable as well as different USB port. You can even attach the drive to another system.
If the problem persists, you will need to use some data recovery tool:
http://www.tomshardware.co.uk/forum/id-1644496/lost-data-recovery.html
Another thing you can try is the Ubuntu Live CD approach. Ubuntu sometimes deals better with failing drives than Windows:
http://www.tomshardware.co.uk/forum/267999-32-recover-data-mode
Just boot up Ubuntu from a flash drive or a CD -> access the problematic drive -> back up all the data -> unplug the Ubuntu drive and switch back to Win.
After all these, you can test the drive and see what is wrong with it:
http://www.tomshardware.co.uk/forum/282651-32-best-diagnostic-testing-utility
Let me know how this goes,
D_KnoW_WD