Many TVs will turn off by themselves after a certain amount of time. If this is interfering with your WindowSight experience, you may be able to change these settings:
Check Eco Mode
This setting switches the TV off automatically after a long period of time without signal or user interaction. You may be able to disable the Auto Power option.
Check Sleep Timer Settings
The Sleep Timer sets when the TV is going to switch off regardless of the user interaction or the signal. Select the desired amount of time or disable this setting.
Check OS Updates
If your TV continues to switch itself off, check for updates of the Operative System, in case this is caused by internal issues.