Press and hold the power button for about 20 seconds
Release the power button
Wait for the Kindle to restart
If it does not restart, press and hold the power button again for 40 seconds
Release the power button and wait for the device to reboot
If the screen is frozen, connect the Kindle to a charger and try again
If needed, go to Settings
Tap Device Options
Tap Restart
Confirm the restart if prompted