I'm not Al, but...

Yes, a humming noise from the motor without movement is frequently a capacitor...
Whether the motor is internally wired for low speed and externally for high speed, will determine the other part of the question. I think most motors internally are wired for "normal", which is max rated capacity, so the external capacitor is probably the bad one...
Do you have an electrical meter that reads capacitance (farads, I think)?
with the right tester, it's easy to check... and many are easy to replace as long as you have a parts source...
Good Luck!
Madwil