A computer can be powered on manually by reaching inside and shorting a particular circuit.
Modern computers operate on a power supply that is controlled by logic circuits on the motherboard instead of a physical power switch that controls power. The motherboard always has power and can detect the press of the power switch because the switch is hooked to a small pair of contacts on the motherboard. A computer can be turned on by creating a momentary connection between these two power contacts directly on the motherboard without the need for the power switch.
Instructions
1. Remove the case cover from the computer.
2. Remove the cable marked "Power SW" or "PSW" from the front panel connectors on the motherboard. The cable is typically connected across pins 6 & 8 of the front panel header pin row on many motherboards. Consult the motherboard manual or the website of the motherboard manufacturer for the specific location of the power switch connector on a particular motherboard.
3. Touch a small metal object onto both of the pins that the "Power SW" or "PSW" connected to for a moment in order to power on the computer.
4. Power the computer off using the software shutdown interface or hold a metal object over the same two pins for about six seconds until the power shuts off to force the computer to power down.
Tags: power switch, front panel, metal object