Huming...
Obviously the motor or part of it is getting power, but no rotation for some reason. Several things could be doing this, and the only way to check is with some dismantling.
Pull the pump off and see if the impeller can be rotated and nothing is blocking it. At this point with the pump off you could try running the motor again. If still nothing take the motor off check that it spins freely along with the transmission. The transmission should turn with great ease counter clockwise (agitation)and some minor hesitation/resistance at first in clockwise(spin).
If all rotates freely by hand without stalling run the motor by itself off of the transmission and pump. If it hums than the problem is electrical or with the motor itself.
At this point a known working DD motor might help, and a volt/ohm meter will come to the rescue more than anything else.
Hope its a quick fix, best of luck here!