When there is a memory module mounted in a memory slot, a memory power circuit provides a voltage to the memory slot. First and second power pins of the memory slot are connected. A first electronic switch is turned on. A second electronic switch is turned off. A programmable logic controller (PLC) outputs a first control signal to the memory power circuit to output the voltage to the memory slot. When there is no memory module mounted in the memory slot and the motherboard is powered on, the memory power circuit provides a voltage to the memory slot. The first and second power pins of the memory slot are disconnected. The first electronic switch is turned off. The second electronic switch is turned on. The PLC outputs a second control signal to control the memory power circuit not to output the voltage to the memory slot.