Like most tech hardware, the Kindle Fire may lock up and freeze from time to time. If tapping on the screen or using the Power button normally doesn’t work, give these steps a try.
Whenever the Kindle Fire freezes, you should be able to press and hold the “Power” button on the bottom of the device for about 20 seconds. In some cases, you may have to hold it down for a full minute. The screen show eventually turn off.
Once the screen goes off. Release the Power button, then press it again to turn it back on. Your Kindle Fire should then restart without a problem.
These steps should work with the original Kindle Fire, as well as the HD and HDX models.