The auger motor some times works and sometimes doesn't

 One of the most common problems we see with this unit is the dispenser door and motor failing.   If you are able to occasionally make the connection to get to to dispense for you I would have to lean towards replacing those parts.  The repair is fairly easy to perform and Whirlpool now sells all the components in one kit.   
 Another possibility  is a failure within the auger motor itself.   Occasionally we have seen where the casing on the motor has had a crack in it, or has not been sealed completely out of the factory, and this allows moisture to seep in.   Over time that moisture can freeze, tying up that motor.    Usually that repair also has the complaint of a humming or grinding sound that goes along with it, not the silence you are getting.    
 If you can occasionally get the unit to work, I would double check all of your harness connections before replacing parts, you may simply have  a loose wire connection too. 

Good Luck on the repair!