Hi, My name is***** will assist you. I am sorry to hear that you are having this issue. Unfortunately this sounds like the display has a developed a fault, if that is the case then it will be better to purchase a new or refurbished replacement.
Another possibility will be a glitch in the firmware and if so it can be resolved by a forced reboot, then your kindle will work normally again. Slide or press and hold the power switch for 40 seconds then release. Then power on and check. If it is still there then it will be a hardware fault.
You can read you books from another device or computer while you are getting the kindle replaced with the Kindle app which is available for most major smartphones, tablets and computers. That means with your free Kindle reading apps, you can buy a Kindle book once, and read it on any device with the Kindle app installed.
Please let me know if you need any other assistance.Please take a moment to rate my service positively.Thank you very much!