Welcome to the forum!
Did you do anything to your setup between when it was working and when it stopped that you know of? Perhaps your boys did?
It could be a number of things. I'd start by checking the volume knob on the sub, the subwoofer output setting on the receiver, the speaker settings on the receiver (make sure they are set to "small" - but I'm guessing they are because the sub light turns on), and the crossover knob on the sub (turn it to the highest number).
I haven't found a manual for the sub, either, or pictures of the backpanel. I'll keep looking.