No matter what caused your problem, apparently, right now, you have no choice but to format this hard drive. However, format process will wipe all your needed files. However, there is no need to worry.
You can easily recover your files back with the help of a hard drive recovery freeware when your drive is asked to format. This freeware has a “Format Recovery” option that is specially developed to cope with these similar problems. Moreover, it really works well since it helped my friend retrieve all his data from a hard drive. It is worth a shot.
Note: You should never format this drive before you recover the files. Otherwise, it will become really difficult to recover your data completely.
You should learn a lesson to back up your data regularly in the future.