To expand on Larry's comment: When he said to "plug it in," he didn't specify precisely where. As he mentioned, it should not be attached to the "B" speaker outputs (if that is in fact where you had it attached before).

At the risk of getting too basic here, look for a dedicated RCA ouput socket on the back of your receiver that is identified for the subwoofer. It might also be identified as "LFE." Hope I didn't bore you. -Bruce