Cancel "Installing the latest software" process at reboot

I had just finished rooting a FireTV, and after executing Towelroot and SuperSU I walked away from the TV for a few minutes. To my dismay, when I returned the FireTV had rebooted itself and was displaying "Installing the latest software." I quickly unplugged it...Seems the process I used to block the Amazon domains on my ASUS router (using the firewall feature), didn't work. Now I'm at a point where every time I boot the FireTv, I see the black and white Amazon logo, and then "Installing the latest software." I thought that Alt+PrtScr+i would break it out of this loop, but I can't seem to get it to work. Is there a trick to it when the FireTv is in this "Installing the latest software" state?

Is anyone aware of a method of canceling the "Installing the latest software" process at reboot? I do not have customer recovery installed. I was on stock 51.1.1.0, rooted, with SU, and the FireTv decided to try and update itself. I'd really appreciate any help or ideas you have to salvage root.

Thanks in advance,
TornSack