Are the lights flashing on the controller, indicating a code in the system? Can you turn the key back just a hair and get the fan to work? Do you not have high? Do you have a bag in the blower motor? See if you have power to the blower motor...this way you'll know if it is a sensor not allowing the controller to (or the controller itself not allowing itself to) send a signal. You have soooo many sensors that play into this system. If you have power to the fan, and it doesn't work, well then you need a blower motor. If you don't have power you get to back track, and without the benefit of knowing the codes, it will be hard.

Chris