Click on Start --> In search box, type control folders and press Enter.
[If you are using Windows XP then type control folders in Run and press Enter]
"Folder Options" will be opened. Click on the "View" tab.
Now select the option "Show hidden files, folders or drives" and uncheck the
check box "Hide protected operating system files" --> Click on "OK" button.
Now look for your files in your external drive.
Later undo the changes you have made by once again going to "Folder Options"
--> Click on "View" tab and click on "Restore Defaults" button --> Click on "OK".