Maybe the screws that hold the VESA mount to the tv went too deep and hit a ckt board.
I have a big plasma (60") that stopped working in November. I opened it up, bought used replacement boards off ebay, and replaced them one at a time until the problem went away. Cost me less than $100. I realize you've moved on (with your new TV), but I thought I'd mention my story so others know you can fix these things.