If you press Home - Menu/Settings - Initial Settings - Sensor List, do you see anything listed under CanBus Sensors?
It should show all sensors on the NMEA2000 network. If other sensors show up, just not the DST, then the DST could have failed or have a bad connection. If nothing shows up then it's likely the power to the NMEA2000 network or the NMEA2000 connection to the TZT.
The above is step one.