I'm sorry about the issue. Please try the following fix:
1. Press and hold the Power on/off button on the kindle for about 30 seconds, then turn it back on and check.
2. If that does not work, go to the Wi-Fi / wireless setting on the kindle, and make sure it is connected to your Wi-Fi/wireless network name and check.
3. If needed, disconnect the power cord(s) from your internet / wireless modem/router device(s) for a few minutes, then reconnect, and check the kindle is still connected to your Wi-Fi/witless network name, then check.
4. If needed, go to menu / settings / account ... option on the kindle and make sure it is registered to the exact email address you've used to ordered books online.
Please reply back to continue troubleshooting. Thank you.