If you are getting no sound from your subwoofer begin by disconnecting the subwoofer from the back of the receiver. Next, run your finger over the tip of the cable and you should get some feedback or a humming noise. If you do not hear a noise there may be an issue with the cable or the subwoofer.
If you do get feedback make sure you plug the cable back into the Subwoofer Preout. Then do a level calibration for your receiver and see if you get the low level rumble from the subwoofer.
If there is no rumble or you got no feedback to begin with try doing a reset which will return your receiver to factory default settings (please view our blog post about doing a reset before proceeding). If there is still no rumble after the reset, the unit must go to a service center to be checked out (view our blog post on located an authorized dealer or service center or you can call us at Product support: 1-800-229-1687).