If you are experiencing issues with the functionality of the 851N, we would initially recommend disconnecting the unit from power before reconnecting.
If this does not solve the problem you are facing or you would simply like to set the unit up from scratch; it may be best to fully reset the unit.
There are two ways to factory reset the 851N but both methods achieve the same result.
The first option is to simply select 'Factory Reset' in the 851N Settings menu.
The second option is to power on the device from Standby with the select knob pressed in. Keep the knob pressed in until 'Factory Reset' appears on the screen.