pull it out of the box that its in check the wiring. look at the tinsel leads connecting to the cone, depending on woofer. over time a tinsel lead may break off and causes the woofer to stop working but this is very rare. check it anyways. woofer could possibly be blown. take a meter to it and check the ohm reading on it. if its a dual coil woofer check each side and see if the ohms are what they are suppose to be. if you need help i will guide you through it.