Help!! This morning we woke up to a freezing second floor. It is on a second unit, and when I went upstairs, the thermostat has no reading at all... no power. I checked the breaker and all was fine there. Is there an exterior switch on the unit that could need to be powered up?

Do you know if your stat requires a battery? If it is a digital readout there is probably a battery and you should see some display of info no matter what the temperature is in the room.