Now you don't say what generation Kindle Fire you own. If it's the very first one then if the cover is too large and you have to make the cover smaller but on the newer Kindles from 2013 and up the problem became the opposite. It usually means the cover is too small or the wrong size when they don't show up. I use 1066x1600 now and it always shows up.
When I upgraded from the very first Fire I had to literally redo every cover to the new size to get them to show up because I had shrunken them so they would display on my old Fire. Don't you just love Amazon?
