hello. My name is***** can help you with your question.
It sounds like your tablet is in need of a complete reset. A full reset will white the tablet and allow it to re-download e-books from Kindle. If you are just using the Kindle app, you should be able to accomplish the same simply by uninstalling the Kindle app and clearing the data from it and then reinstalling it. To do this, go to the settings on your tablet and then scroll down to apps and under the apps select the Kindle e-reader and then select uninstall. It will verify that you want to uninstall so except that and then once it is done, go back to the place store and install the Kindle reader. Then when you open up it should go through the initial set up again and synchronize your books. If not, or if you have any questions, please let me know.