Test the subwoofer by unplugging the RCA cable from the receiver, with the subwoofer plugged in, turn the gain up to 2/3 up and tap on the end of the RCA cable. Do you hear a buzz? If so, then the subwoofer is working fine and it's an issue with the receiver settings or it's subwoofer output signal.
If not, then try replacing the RCA cable and see if this works.
Lastly, what is the make and model of receiver that the subwoofer is connected to?
Okay so there is no buzz at all when tapping the cable correct?
Can you hear any hum or any noise at all coming out of the speaker?
If you shut the subwoofer off, can you hear a little thump from the speaker?
If not, then it's likely that the Digital amplifier failed in the subwoofer and this is why you're getting no sound from it.
The amplifier is faulty then. You would either need to have the amplifier repaired, replaced, or you could also purchase an aftermarket plate amplifier and install it yourself. I can help you with whatever course you'd like to take.
Yes, here is the contact information for Infinity's service center locator: