Inifinity Entra Sub not working

I have an Infinity Entra Sub for my home theatre system. Well a few (about 5) years back probably about 7 months after I bought it, from CIRCUIT CITY, it stopped working just had a loud annoying hum. so i took it back to get it fixed I bought a 1 year warranty for the sub and polk audio surround sound speakers and they tell me that I only bought the extended warranty on the surround speakers not the sub and they told me I would have to send it back to INFINITY to get it fixed but I wasn't going to pay the shipping to get it fixed. So it's just been sitting here unplugged and I figured I would tear it apart to see what the problem is. Well I hooked it up today and had the HUM so I unplugged the speaker on the inside and checked to make sure the speaker works and it works fine so the problem must be inside the amp, well when I hooked the speaker bac up there was no more hum, but it still won't produce any sound.

Anyone know what my problem could be?