My brick is dying. Upon start up my XBox One shuts down after about 2 seconds of being on and the brick shuts down, too. I've fought with it all night trying all the tricks above. I got fed up, walked away (with a dead brick still plugged in) and came back about 20 minutes later.
I unplugged the plug from the brick (not the wall), turned the XBox One from flat to vertical, waited 10 seconds, banged the brick against my knee for good measure, put the plug in the brick, and laid the brick upside down instead of the normal position. I waited a second, said a prayer, then hit the on button on the system. It fired right up and I'm about to play CoD WWII.
I know it sounds crazy but this is exactly what I did and it worked. Don't know if it was the brick banging, turning the system vertical, or flipping the brick upside down. All I know is it's working now.