Hello, my name is Rusty. It is possible that your Kindle is full, and you'll need to clear some books before adding new ones. Don't worry, deleting your books only removes them from your Kindle, your books are all stored online.
To get your books on your Kindle now, there are two ways to do it.First, from your Kindle, click your "archives." There you will see all the books that are in your cloud. Click a book, and it will download (you have to be connected via wifi to do this).Second, you can go to your "Manage Your Kindle" page (link is at the bottom of any Amazon page) and click "actions," then "deliver to my" and choose your Kindle.