Try a hard reboot before you try sending it off to be repaired. Make sure your Kindle is charged. Hold down the power button for 25 to 30 seconds (ignore any messages you see). Let it sit for about a minute after and then hit the start button like you normally do to start it off.
From time to time my two Fire's won't start (probably because of something I should not have done). Using this procedure has brought them back the few times this has happened. Give it a shot. fdalbor