A warning circuit is configured to output a warning in response to an integrated graphics card unit being coupled to a display screen and a discrete graphics card being coupled to a first connector. The first connector is configured to output a coupling signal in response to the discrete graphics card being coupled to the first connector. The integrated graphics card unit is configured to output a control signal in response to the integrated graphics card unit being coupled to the display screen. The warning circuit includes a controller that controls the discrete graphics card to convert display data to drive the display screen in response to receiving the coupling signal. The warning circuit is configured to output the warning in response to receiving the control signal and the coupling signal.