PDF thumbnail is not displaying

I am quite new to Drupal (started using in Nov 2011) so this might be something I'm doing wrong. Yesterday I had set up PDF to Imagefield for my PDF's working (at least it was displaying a small thumbnail of the pdf when I added content. After adding about 5 data records that included these pdf's I went to Views to make a grid view so that I could see all of the PDF's thumbnails on a single page and noticed it was only displaying the name of the PDF not the image. I went back into the Structure>Content Type to edit the field but it looked OK, so I added the next record and at that point of time the PDF's started to display the filename - just like it looked in the view. So I tried to work in display suite under the option of how the pdf is displayed (Options are: Generic file, Table of Files, URL to file, PDF view,or PDF link) I selected PDF View. The PDF is still only being displayed as the file name no longer the thumbnail image - Can anyone point me in the right direction? I really appreciate any help!