Btw, TestDisk is a very powerful tool and any incorrect use of it may destroy your data. Only use it if you know what you are exactly doing.
Anshad Edavana's suggestion that you should try to recover data first is good advice and there are several ways to do that including the Puppy suggestion but I'd like to address the statement that I quoted.
TestDisk can change your partition table or perhaps the boot sector (and file system if you dig into the advanced menus) but it goes to great lengths to avoid damaging the data on the disk.
What can threaten the data on the disk are things that can overwrite data on the disk (like CHKDSK) and more importantly physical damage to the drive that may continue to do damage as you attempt to recover or repair the drive.
Of course, the safest course of action would be to send the drive to a professional data recovery lab. If you are not able to do that then the first thing that you need to do is attempt to determine if there is any physical damage to the drive. This would help you decide the best path to a potential recovery.
Get a copy of GSmartControl for Windows (I'm assuming that you have the drive connected to a computer that is running Windows)
Unzip it and run gsmartcontrol.exe
Double-click your bad drive and click the VIEW OUTPUT button and copy and paste the resulting report in your reply so we can look at it.
Let us know if you have any difficulty doing this.
-=[ James ]=-