Why does my car amp not have power coming out of the speaker out put?

I have been running this setup for a couple months now and I took it to the dealer to have it serviced and I waited in the store for about three hours and after I got my car back the subs didn't sound nearly as loud. I think they blew something in the amp. Because after a while it started getting quieter and quieter but never any protect mode. I checked all the connections. The pre amp rcas are working. I used a multi meter to test power the amp has a constant 12-14v and so does the remote the ground has also been tested and is connected directly to a piece of metal that has been sanded. But when I test the power coming out of the amp through speaker output there is no voltage. Is the amp fried or is there something I am missing?