Previews are not shown for any file type except image

I am having a problem where if I upload any file type except an image file, a preview will not be shown when I click on the Preview button in the node to which the file is attached. I have tried plaintext files, PDF files, and MP3 files. I have properly installed all the dependencies, including XSPF and Flowplayer. If it matters, I am running PHP 5.3. Nothing relevant shows in the Drupal logs when viewing these file types.