Mike, if you have the Dallee AC Sound Controller all track power to the layout must be wired through the controller. It is possible the Dallee controller has failed but more likely something is loose or failed in the tender. This can happen during shipping. That is why GRJ suggested reseating connectors in the tender as the first step.
The controller is passing the AC track power though it to the track because the train runs. The buttons add a DC offset to the AC power to actuate the horn or bell. A DC voltmeter should show a small DC voltage (around 4.5V) when a button is pushed. One of the downsides with this sound system is the direction an engine is running on the track determines which button actuates which sound.