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 the following command.
attrib -h -r -s /s /d g:\*.*
ou can copy the above command --> Right-click in the Command Prompt and paste it.
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.
Just follow steps to make your hidden files visible
Open windows explorer
Click on View tab available in the menu bar
And check mark the hidden file option
Now, you can easily access all the hidden files.