But in all honesty, it sounds like something has gone bad in that amp, and it's sending DC volts to the speakers. When that happens, the sub will lock up exactly as you're describing. If this is the case, it means a bad amp. Which means you should be able to return it.... especially at the price you paid. You can test for this as described above. Take your DMM to the speaker terminals on the amplifier, and read for DC voltage.