@Katie1: Did you select On Device, All Items and Recent on the home screen?
If so, the Kindle might have gotten stuck indexing. Try the following:
- Connect your Kindle to a PC and delete all directories and files in the following Kindle directories:
E:\documents
E:\system\Search Indexes (You might have to unhide system files to see this directory.)
- Select Settings > Restart
- Transfer your books to your Kindle with Calibre or download them via WiFi from Amazon.
(I'm assuming that the Kindle is your E: drive.)
If you still don't see your books, you'll have to reset your Kindle.