If you are using Windows 2000 or XP (maybe ME), you can just right click on the folder they are all located in and go to "properties" on the menu.
Uncheck "hidden" and press apply. Depending on your collection, it might take a short while. If "hidden" is not already checked, or half-way checked, then check it and uncheck it again, then apply.
Just an alternative to the method mentioned above.