Have you confirmed that, according to your owner's manual, the settings in the receiver's speaker set-up menu are correct (for example, subwoofer is set to "on" or "yes", etc.)?
Is your sub plugged in and powered on? Is the "FILTER" switch set to "off"? (This disables the sub's internal low-pass filter (a.k.a. "crossover"), which is what you want given that the receiver is handling all crossover functionality.) Set the level of the sub to "noon" position to start.