Please count the number of blinks when it shuts off then reply here to this topic and wait for my reply. Do not open a new question or relist the question.
Six blinks means there is a failure on the "A" board. Unfortunately the board is no longer available so individual parts have to be soldered onto the board. A repair shop will charge about $400-$500 to do this. They may have to pull the board out of the Tv, take it and ship it out to a special company that rebuilds these boards, then re-install it after coming back from rebuild. This can take up to 6 weeks.
If you have questions about this answer then feel free to reply here. It may take a few minutes for me to be notified of your reply so please do not start a new question or relist your question.