Hi. Have you tried resetting the unit?
Resetting your Kindle Fire can solve intermittent problems. To reset your device:
Make sure your device is disconnected from any power source.
Press in the power switch and hold it there for 20 seconds.
The screen should turn off, once the screen is fully turned off press the power button in for 2 seconds and release. The device will turn back on and you will see the Kindle Fire loading screen.
This reset will not affect any books or content you have on the Kindle.