Keyboard backlight does not work!?

I have a MacBook Pro 15" 2.4 GHz (Penryn). I need to know if I should replace the ambient light sensor or the inverter cable/LED board? My screen brightness works just fine, the caps key on my keyboard lights up when pressed, but the rest of the lights on the keyboard do not light up at all. I have tried multiple times to adjust the brightness both on the keyboard using the F5 & F6 keys and in the system prefs pane, with no success. I have also checked to make sure all cables and wires are connected properly, and they are. So which one of the above 2 should I replace to get my keyboard to light up again?