Thumbnails not showing in Explorer in Windows...

Question

Recently my thumbnails for all image formats (except .ico) have stopped appearing in Explorer in Vista. I have unticked the "Always show icons never thumbnails" option in the Folder and Search options. I have set the visual effects to be for best appearance. I have reapplied the Aero theme. I have also tried deleting thumbs.db and the icon cache. I do not know what else to try. Any help?