A lot of TVs automatically turn off if no buttons are pressed or 1,2 or 3 hours, there are also 'sleep timers that can be set.
Have a read here and see if any of the suggestions work:
[link|https://www.sony.com/electronics/support/articles/00032613|https://www.sony.com/electronics/support/articles/00032613|new_window=true] - particularly read '3. Check the settings of the TV.'