Not working on any speed ?, I would check the basics first, fuses, then check power supply at the switch and the earth on the heater motor itself, all of which can knock out all speeds, for it to be a resistor problem it would be on the slower than full speed positions where the resistor is actually used.
I've no idea where it is on your car, but know a man who does, if you phone 01603 866999 you will get through to FOCUS/MONDEO PART, who of course know these inside out as that is all they do, ace source of spares as well.
tabetha