On the SHIELD TV Home screen, select Settings 
.
Under "Device," select Screen saver.
Select When to start.
Select one of the options.
SHIELD TV will automatically go to sleep after the time period:
On the SHIELD TV Home screen, select Settings .
Under "Device," select Screen saver.
Select When to start.
Select one of the options.
To restart:
On the SHIELD TV Home screen, select Power 
and "Restart."
If this is unsuccessful, you can also unplug the power cord, wait 10 seconds, and then plug the power cord back in.