This hard drive recovery freeware can fix your problem for you. Tips：
1. Do not store any new file on this drive to avoid the original data overwritten by new data, which can make it gone forever.
2. Do not save the recovered data on the same drive in case of recovery failure.
3. Do not forget to format this drive to see whether it could work as before.
4. Do not forget to back up your important data regularly in the future.
I was in the same problem that you are talking about...My external hard drive has been corrupted due to virus attack that is why I was not able to access my important data from external hard drive. But thanks to my friend who suggested me a software named Disk Partition Recovery, which is proficient in usb hdd data recovery. If you need it you can download it from the below provided link.