How important is the inner data on this external hard disk?
If the inner data is not so important for you, you could directly format to see whether it is recoverable. Or you could take this chance to replace it.
But, if the inner data is VERY important for you, you could try a hard disk recovery freeware that has ever restored all my work files back. You could download it here: http://blog4mark.blogspot.com/2012/10/convert-external-hard-drive-to-ntfs.html
In the future, you should learn to back up your important data.