Hi there and welcome
First as this is usually corruption, are you on a windows computer? and if so, which version and which Drive letter is the drive appearing as?
Which version of windows please?
Just so I can give the instructions
no sorry, the version of windows, eg: XP, Vista, 7,8,10?
Press the windows key + X and click on Command Prompt (Admin)
A blank window opens
chkdsk l: /r
Let it complete, may take some time and when it has then attempt to recover the files using Recuva from here (its free)
Click Download Latest Version on the Green Button top right
If the files can be restored, this process will get them
Let me know the results please