Have you checked to see if it runs on high? A blown resistor will take out all low speeds except high. I would start by putting a voltmeter on the lead to the blower. If you have voltage, the blower motor is bad. If you don't, you'll need to work your way backwards.
Pull the motor out & see if it spins smoothly by hand. Wash & brush all the dust & lint off the wheel, and shoot some oil into the motor so it can soak into the bearing at one end for a few hours, then flip it & do the other. While it's out, vacuum out the evaporator fins & the resistor.