My digital thermostat has shut off after a power failure. There is absolutley no display appearing. I pulled the thermostat off thinking maybe the batteries were no longer working but came to find out that the thermostat does not have batteries. I then went and bought a brand new thermostat that does have batteries for the display but when I properly installed the new one, the display worked (of course because of the batteries) but niether the heater nor the airconditioner comes on when I tried to set the temperature to have it come on. I also tried the Fan On option and the Fan won't even come on. Of course before I went and bought the new thermostat I checked the breaker to the AC and turned it off for a few minutes but that didn't help and I also looked next to the actual unit outside and did find a box attached to the house and thought that should be the individual breaker for the unit but when I opened the box there was no lever to trip inside or on the side of the box, just a wierd looking black hook looking think that had ON, OFF on it.The only thing I could do with that is pull it straight out toward me and I turned it aroung in my hand and inside of it was like some metal prongs that locked it in from where I Pulled it out from. What else can I do or can you please tell me where I can find something I should trip (like a breaker) on the actual AC unit. HELP! Any suggestions? I am not sure of the unit model number because I am at work. I just picked on from the list. The unit is only 4 years old Mine is a similar kind of problem. In my case, my thermostat was not working properly (the setting used to change automatically) so I bought a new thermostat (sc2010) same model as the bad one. I installed it and I am pretty sure I put the wires correctly as stated. After the installation when I turned on the power there is no display. I also tried installing the old one again but there is no display. Mine is Lennox unit. Any help is appreciated.