I would suspect it overheating, but I would need detail on the condition of the room its in, how long it on before it goes off, etc.
It could overheat "overall" meaning it could just be so hot the TV just shuts off, or a specific component is overheating like maybe it works longer if its displaying lower resolution devices like Gaming consoles and if switch it to a device that will display at its max it resolution like blue ray player it will kick off sooner. Or it could be the Power supply in the TV could be failing. Is it plugged into the a power strip then that could be the culprit.
So I gave a lot a details with possible reasons why ... this how ever is the opposite of your question which extremely vague and general.... The Title...