Help! E72 error out of the blue

[mmritter]

Please help, I have a toddler I have to get to bed tonight in 2 hours and I can't figure out what is wrong with our NEST as the temperature is dropping. I've never had this error in the 6 years we have been here, but I got an E72 error telling me my HVAC isn't connected. It was running fine this morning, house has power, the Rc and Rh wires are connected but the diagram shows them in red...

[Patrick_Caezza]

@mmritter 

You said you have both the Rc and Rh wires installed. Do you have separate heat and cooling units?

The E72 error means the thermostat is not getting any power on the  R wires which is normally caused by a power problem in the HVAC furnace/air handler. 

Check that the HVAC unit breaker. Has it tripped?

Make sure the covers are on the Furnace/air handler correctly.

Check the fuse on the control board in the furnace/air handler.