I have a Bryant furnace about 10 yrs old. This is a furnace/central air unit located outside. The fan in auto posistion would not come on. Switched to on position and furnace lit and fan ran. Turned to auto and ran for several seconds and went off. Now on auto nothing works but if I turn the fan on the on position the fan runs but I have no heat. For your information I am a female with some common sense but if you would help keep the terms simple it would be appriciated. Really cold here. I thank you for any assistance.