The blower resistor can fail and give you nothing, 1/2 speed or full speed, it depends on which type you have. The heatsink looking ones can fail and only work on low speed. Get a multimeter and test the fan terminals for resistance, if you get open circuit then the fan is dead. If you get resistance, use your multimeter to back probe for voltage on the fan plug with it plugged in and turned to full. If you get nothing then move onto the blower resistor.