Same thing happened to our system. Out unit was a new leftover, so warranty was over (sigh). Our system is a Zone Defense-name is on back of monitor. If it is, contact them (service person named Woody) at the number on this site (Zone Defense LLC
). Company fixed unit under warranty N/C and even shipped it back free. They said there was a thermistor that was failing in the units and they would be intermittent, go "blue" and then go off, but the green light would stay on. Only way to restart was to kill power (ignition) and try again.
Hope this helps.