It seems that your drive is corrupted. Therefore, in order to retrieve your data back, you should try a hard drive recovery freeware to help you: http://www.squidoo.com/usb-drive-recover
Honestly, my WD hard drive was corrupted last month. It was really urgent because of the large amount of important work files on this drive. However, fortunately, I tried this freeware recommended by my friend. Now, I have saved both of the data and hard drive. It is really worth trying. Note for you:
1. Never attempt to put any new data on this drive in case of rewriting the original data.
2. Never try to store your recovered data on the same drive in case of recovery failure.
3. Never forget to buy a new one to replace it.
4. Never forget to back up your important data regularly in the future.