Try this 1.
May be the files are in hidden mode.
Click on "Start" -->Run-->type cmd and click on OK.
Here I assume your external hard drive as G:
Enter this command.
attrib -h -r -s /s /d g:\*.*
You can copy the above command --> Right-click in the Command Prompt and
Note : Don't forget to replace the letter g with your external hard drive letter.
Now press "Enter".
Now check for your files in external hard drive.