Hi Becca
To delete an image, open the one you want to delete and look in the box below it "Photo Details". you'll see 2 rows of little icons, the 4th one in the bottom row is to move/delete pics. Just click there and follow the instructions.
As for the No Thumbnails, in that same group of icons, there's one that says Hide Image, you may have hit that by mistake, Try unclicking there
Nope, that was wrong
Click on Edit Photo and directly under the space that says No Thumbnail, you'll see an option to Rebuild Thumbnail...do that
