sub not working

cwbslayer137

I have a polk audio mm2104 sub in my truck, the amp i am using for it is the polk audio mono block amp. The stereo was professionaly installed. Recently the sub has stoped working. The amps power button is still lighting up. Yesterday i took a look at it, and hooked up a different sub to see what component was not working correctly. The new sub did nothing. So i put back in the old one, and came to the conclusion that its the amp that is acting up. So i took off the face plate and looked for a loose connection. There are no loose connections. Then i turned on the stereo, and the sub worked for a couple minutes and then stoped again. Is there something else i should check, or is my amp fried?