Jady, the buttons are notorious for wearing out. If u take the switch off, you will see there are 2 wires.
Usually by touching the 2 wires together, its closes the circuit and fires the ball (it might be a closed circuit switch and by pressing the button it might open the circuit and fire the ball as well) but u get the idea.

Take off the switch and touch the 2 wires together, it shld fire the switch, also test and fire the switch/ball shooter in the menu setings and it will also confirm that its a $20 switch issue, and not anything else. Hope it helps.