Hi there and welcome Dianne
Can you tell me please the make and model of the reader?
Where exactly did you purchase the books from? On the Kindle itself
This is usually an issue with the Firmware, so I would first like you to do this please.
Remove the charger from the Kindle and hold the power button to off for 35 seconds.
Release, then connect the charger and try to turn on the Kindle and access your books
Let me know the results please