A keyboard connected to a computer by a USB cable has a power button for use when the computer is in a power-down state to initiate a system power-up operation. The data wires of the USB cable are connected to a first switch in the keyboard and a second switch in the computer. When the computer is on, the switches connect the data wires to respective data lines in the keyboard and the computer such that the data wires can be used for data transmission. When the computer is in the power-down state, the first switch connects the data wires of the USB bus to a power button on the keyboard, and the second switch connects the other ends of the data wires to a system power-up circuit of the computer. When a user presses the power button, a trigger signal is sent via the data wires of the USB bus to the system power-up circuit, thereby initiating the system power-up operation.