I read on this board once that the VGA controller senses if a monitor is present by the load on it's output pins. These are the R,G, and B outputs, and the Hor and Ver Sync signals. You can fool the VGA controller into thinking a monitor is connected by wiring up a VGA terminator plug. Get a 15 pin replacement plug for monitors, and connect a 75 ohm resistor between R and R return, G and G return, and B and B return. Then connect a 600 ohm resistor between Hor and Hor return (or signal ground), and Ver and Ver return (or signal ground). This will fool the VGA controller into thinking a monitor is connected.