I assume you are using Microsoft Windows XP? If you are, try the following assuming that your files are still there but hidden:
1. Open Windows Explorer
2. Click on Tools >> Folder Options
3. Click on the View Tab
4. Under advanced settings, look for the item "Hidden files and folders". Check the radio button for "Show Hidden Files and Folders".
5. Click on the button [Apply to All Folders]. Finally, click on the [OK] button.
That's it. For a graphic view, visit the source site below.
If your files are deleted by some reason, you could download some free file recovery tools and try to recover your files. I've also included the link to discover in the reference source below.