I know it's old, but I bought a Kindle Fire 2nd generation from Amazon a couple of months ago.
It keeps getting stuck, like it becomes completely unresponsive/ unresponsive to touch. The only way to "wake it up" is to press the power button to go back to the lock screen, and get in again. If you do that, it's back to normal immediately, until next time it does it (I'd say around once every 10 minutes).
The fact that you can get it unstuck so easily made me think that it's not some process that starts taking up all CPU, but something else. I confirmed this intuition by installing task manager apps and similar. The Kindle seems to operating under normal conditions. It just gets stuck.
How can I fix this? Is this a common problem with the Fire 2nd gen? It's absolutely unusable.