:cool: Hi my heater was working just fine last night and then it started blowing cold air what can I do?

I have no idea since you did not post the brand and exact model number!

Exactly what is it doing besides blowing cold air?
Did you cycle the power on and off to try and reset the unit?
Is the thermostat calling for heat?

On some furnaces if you loose the low voltage side of your transformer the blower will blow until power is shut off.

So give us more info about what is happening, have you turned the thermostat off? Have you watched your furnace when you turn it to call for heat, it is very hard for us to GUESS what is wrong with out any clues.