The default on the tv is to sleep after 1 hour. So if you didn't turn it off, it will turn itself off after 1 hour. You can change that setting in General > Sleep after > ... The smallest setting is 15 min, 30 min, 1 hour, and up...
Hope this helps.
Regards
Edit: Hold the center select button down for 5 seconds and It'll go off.
Message was edited by: captfred