Some Amazon Fire TV users may find themselves stuck at a screen that say ‘Connecting to Amazon.com’ when trying start it up. The device is unresponsive to buttons and won’t let you go any further. Restarting only takes you back to the same screen.
I have experienced this problem myself. Here’s how I got out of it.
When the Fire TV logo appears, press and hold the “Back” 
button and “Right” 
on the control pad for about 15 seconds, or until you see an option to factory reset.
Once the prompt appears, select “OK“, or just wait for the countdown to finish. The Fire TV will start to factory reset.
Complete the factory reset, and hopefully you’ll be able to go through the setup steps again.