Power to the unit is the first thing to look at.
Check power off of the transformer (24VAC)
Check power in at the thermostat.
If you have power to the unit, then there should be power input to the transformer. If you have power input to the transformer but no power output from the transformer, replace the transformer. If you have power output from the transformer then check for power at the thermostat, if you have power at the thermostat, then replace thermostat, if you have no power at the thermostat check wiring from transformer to the thermostat.
If all you did was ductwork and no work on the electrical system then it is likely a bad luck situation for you. You touch it, you own it. Most likely you will need to get it repaired even though it is not your fault.
If you can get a technician in there and have him troubleshoot the problem and report to the HO that there was no way you caused the issue you could get away with it.
Good luck.