Gas and Oil Home Heating Furnaces - Central natural gas furnace problem

I have a Lennox natural gas furnace/AC unit, about six years old, that is not working. When I set the thermostat for heat, the furnace goes through the regular cycles and ignites the burners. About the time that the blower should come on, the burners go out leaving only the little exhaust fan going. The blower motor never comes on. If I set the thermostat for AC, the outside condenser fan runs briefly and then stops. Meanwhile there is no activity at the main unit in the AC mode. If I set the thermostat to "fan on" there is no response at the blower motor. I greatly appreciate any help you can give!!!!! :D

When does the sytem start up again? After when you turn off the power to "Reset" the system?

What model do you have?

I would almost want to say it's either you control board or transfromer.

How cold is it outside??? The outdoor unit maybe shutting off on low pressure if there is one.