If you do not see any books in your Bookshelf, you have inadvertently created a new account.
Log off and try to log in with your original sign-on and password. DO NOT let the browser auto-fill the password for you. Wipe that out and key it in manually, at least once. See what that does.
If you find you HAVE accidentally created a new account, then, once you're back in your original account, contact KDP using the "Contact Us" at the lower-right of this screen, and ask that your empty account be deleted.