Post Image Plugin

Im trying to get the image thumbs to show up in the post list of a category on the front page. It lets me choose a pic to make a thumbnail out of, crop it and it even saves it, but the posts don’t show the thumbnails.

I think that the theme file may be stopping these thumbs from showing up somehow, but I would just like someone to show me where to start editing to be able to make this happen. or maybe suggest a better plugin. Thanks