A computer system includes a monitor, and a motherboard. The monitor includes a display screen, a switch set on the monitor, and a first video connector. The first video connector includes a first monitor identity pin, and a first ground pin. The motherboard includes a second video connector. The second video connector includes a second monitor identity pin electrically connected to the first monitor identity pin, and a second ground pin electrically connected to the first ground pin. The second monitor identity pin and the second ground pin are correspondingly connected to a power signal line and a ground line of the motherboard. The switch is connected between the first monitor identity pin and the first ground pin, to control the motherboard to power on or power off.