Just moved into a new house and it has the Robert Shaw 9420 system in place. During the warm month the AC worked perfect but since it has started turning cold(low 40's) at night I have been unable to set the temp for the heater. No matter what temp I set it the heater keeps running until I manually shut it down at 79, which means I either get up and down during the night to turn the system on/off or leave it off until I get up and turn it on to warm the house back up... how annoying is that?? Could anyone help me?

Sounds like the thermostat took a dump on the heater side. Probably lightning. Half of those wires if not all, run outside the house. A good reason to have your outside unit grounded.