How can I unfreeze my kindle fire ? - Amazon Kindle Fire HD

Hold the power button for 20 seconds and then let go. Kindle will usually reset.

Have you tried holding the start button down for about 10 seconds, releasing and wait another 10 before starting as normal. It will take a little longer to restart at first but then all should be fine.

"Performing a hard reset on your Kindle Fire may resolve intermittent issues like a frozen screen, battery issues or trouble downloading content to your Kindle Fire. Allow your Kindle Fire to charge for approximately 30 minutes, then try the following steps.
To perform a hard reset on your Kindle Fire, press and hold the power button for 20 seconds and then release. After the device has completely turned off, press the power button to restart your Kindle Fire.
If your Kindle Fire is still unresponsive, try charging your Kindle Fire before trying to reset the device again." from here. Hope this helps, good luck.

Press and hold the power button for fifteen seconds or so, ignoring the "Shut down?" prompt until it shuts off. Release the power button, then press and hold for a second or two until the Kindle starts rebooting.

Press and hold the power button. If it prompts to shut down, ignore it and keep holding the button. It should turn off after fifteen seconds or so. Release the button, then press and hold for two seconds or so. It should start up and reboot. Does it?

Press and hold the power button for twenty seconds or until it shuts completely off. After releasing the button, press and hold it for a second or two until it starts to reboot.

Press and hold the power button for fifteen seconds or so, ignoring any "Shut down?" prompts, until it turns off. Release the button, then press and hold it for a second or two until it starts to reboot.

Hold down the power button for 10 seconds. That will turn it off and reset it.