Furnace fan help

I have a us stove co. furnace m1600. Tonight the fan stopped working correctly. It just barely runs. It has a manual fan speed knob hi, med, and low. I always run it on med. I have tried changing the speeds but fan stays the same barely runnig. When I do change speeds it sounds like it wants to speed up but doesnt. Any help would be greatly appreciated, thanks

How hard is it to turn the fan with the power off?.

It is very easy. You can hear it try to start up at the dfferent speeds, but just doesn't get going all the way.Stays running at just a very low speed, even lower than the low setting on the speed control knob.

It's possible that your starting capacitor is blown. Look for the capacitor and get a number off it and go shopping for one.