If it not a button or switch in the wrong position, then some electrical gizmo may have just given up the ghost.
When you say it 'stopped working' I presume you mean the display is 'off', not that the display is on but the picture is gone.
In this case, check the rear to insure that the power and ground are still connected (on or the other may have become disconnected). If the unit has power connected, measure the voltage right at the display to insure that is 12 to 14 volts. If it has correct power and won't come on, the odds are good that the display is fried.