I got home from a long trip and nothing seems to work. I can't switch on either the AC or the Heat from the thermostat. Cannot get it to turn on from Auto or from On positions.

Help? Any suggestions?

Have you tried shutting the breakers clear off, and then back on again? Sometimes they are off, but don't look like it. Next, check to see if the thermostat is getting power from the transformer in the furnace. Pull the thermostat off the wall. Check for 24 volts between the red wire and a blue one if there is one. If not, with the thermostat not calling for heat, check for the voltage between the red wire and the white. If you don't have voltage, there is a problem with the transformer or the wiring. Sometimes there is a fuse protecting the transformer.

If you have voltage, check again with the thermostat calling for heat. If you still have voltage, the problem is in the thermostat.