It seems that it is the problem of your hard drive. Does assigning a letter fix the problem？
If not, your drive must be corrupted. Go try a free hard drive recovery tool
to get back your inner data and format it to see whether it can be recovered. This freeware is really efficient and easy to operate.
You could download it there: http://blog4mark.blogspot.com/2012/11/how-to-repair-corrupted-pen-drive.htmlNote
: You’d better buy a new drive to replace it in case this situation happens again.
You should learn a valuable lesson to back up all your crucial data on a separate drive regularly in the future.