Press and holding down the power button for 20 seconds or more. Then turn the device back on by hitting the power button again. If this doesn't work the first time, you can try holding the button down for 30 seconds or more. Most of the time, this will be all you have to do to make the Kindle Fire work again.
I think yes, you have to press the power button for some time in order to turn the Kindle firewall off. Then turn on the device and I am sure the issue will be resolved. I think it happens mostly due to the systematic errors. It is what we can do to remove the errors.
I just adore my Kindle, but I also had same issues with turning it off on a several occasions. I have also found solution in pressing off button for some period of time. Although this solved the issue, I was just wandering if this is introduction to some bigger problem with Kindle