What exactly 'stopped working'?? We need more info...

Did the ventilation fan quit? Then look for fuses (well, you already did), or wiring to the fan switch. Or the fan-speed resistor.

Does the air blow cold instead of hot? Then look for stuck-open thermostat or low coolant... Or maybe a broken wire from the temperature knob to the actual valve.

What's your temperature gauge read while this is happening?