My unit is about 14yrs old. We just had siding put up so the box was removed and then re-attached. The unit worked last night, however, when I came home tonight it was not working at all.I checked the circuit breakers (set and Rest), changed the batteries in my electronic thermostat. With a volt meter I checked the fuses in the outside box(good) and the unit is getting volts to the unit. There is no sound coming from the unit at all. I didn't open the unit up as it was getting dark. I would like to narrow down the possibilities myself, I have had electronic and mechanical training, however, I have to say I don't know much about HVAC. How can I narrow down the possibilities, Thermostat, Motor, Fan?

This unit is acutely only 9 years old.

How did you determine that the unit was getting power without opening up the unit (removing the cover to electric components) although it is probably a right guess
In the daylight you need to determine if there is low voltage (24 to 28 ) going to the contacter. If not start tracing the small tstat wire slowly looking for breaks back to the furnace if OK check the transformer for output
Let us know from there what you`ve found