if you press the screen can you see the green light on the controller box get brighter as you press it?
IE it should be on, but go brighter if you press the screen.
if it does this, it may just need to be recalibrated. next to the service button is a calibration button. if you press this in the game select screen, it will bring up some marks you press to calibrate the screen.
if the machine ignores the press, you might have a data cable issue. make sure the cable from the controller box is plugged into the motherboard's com1 port.
if it accepts the calibration, but in testing the mark doesn't go where it's supposed to or gets stuck in one spot, you may have an issue with the touch overlay.