X1 stuck in reboot loop

Had to unplug X1 system yesterday and after plugging back in, X1 box is in a constart reboot loop; never gets to Welcome screen, only black screen. All other TVs in the house work w/no problems and all apps (e.g. Netflix, Prime video) work, but cannot watch cable TV (e.g. CNN, etc.). Have refresh/restarted via internet, and box reboots, but nothing on screen. Have done ALL the usual troubleshooting steps but to no avail. Have even tried exit>exit>exit>720 to see if "black screen" was the issue, but it's not. Suspect it's X1 software, but only a guess.