New TV won’t boot up

I bought a brand new 65” LG tv. I got it home and set it up but when I plugged it in the LG logo popped up and the red light was on. Then the coloured circles began and then the screen went black and shut down. This just kept repeating. I moved the tv to the bedroom and it started right up and set it all up. So we carried it down the hall still plugged into the outlet in the bedroom on a extension cord and the tv still on. As we were just about to enter the living room the screen went black and started the LG screen the circles and $@$* down and started up repeating.

I don’t understand what is happening. LG support just kept telling me it’s the power supply despite telling them I never unplugged it and as I moved it back into the hallway it started up again?

nobody has any idea what is going on