When the resistor fails, you normally lose all speeds except the highest speed. I would get this checked to see why you only have the lowest speed, it may be the switch. What happens when you select a higher speed, does it continue to blow at a slow speed or does it stop working?
Hi, This isn't consistent with a bad resistor, but that doesn't mean it can't be the resistor. Since the symptoms are so odd, I would suggest you get this diagnosed. Let us know what you end up finding out!