Power lead

Hi, is the Xbox power lead connected to a surge protector or power extension lead at all ? If so try connecting the Xbox power lead directly to the mains power outlet. As things worked ok at the shop it could well be simply having the Xbox connected directly
to a mains power outlet.

Yeah, it's a very sloppy connection on mine. You can use a regular computer power cable. The one I tried had a proper, snug fit. It's the same configuration, just doesn't use the ground. (I know there are people on this board claiming it's different.
It's not, other than the fact that it doesn't use the ground wire.)

To be clear, I'm talking about the cord from the wall to the brick, NOT from the brick to the XBone.

Hi, try powering the Xbox off, take the power lead out of the mains power outlet and press the power button on the Xbox several times, reconnect the power lead to the mains power outlet and then give things another try.

Could you power the tv off, remove the power lead for the tv from the mains power outlet, press and hold the power button on the tv for 30 seconds . Wait 10 minutes and then reconnect the power lead and give things another try.

Do you use a surge protector or power extension lead at all ? If so try connecting the Xbox power supply directly to the mains power outlet, It could be that the surge protector or extension lead is dropping power which would cause the Xbox to power off.