Basically I want to make sure your gamepad is actually connected and buttons are registering.
In debug mode, on the bottom left look for the game pad object. Click it and you'll see a field that says "Last button" on the right. Now when you press buttons on your game pad, that should change. If it doesn't, that means your game pad is not sending any signals to the program, which would explain why on button pressed does not work.
If it does change, then I'll have to think of another reason
Edit: I meant trigger as in shoulder buttons on some game pads.