You can test a computer's power switch in a few steps.
A power switch on a modern computer is a momentary contact switch that can be tested by removing the connector from the motherboard and attaching it to a multimeter. Older computers used rocker switches or push button on-off switches which can be tested in a similar manner, except they need to be manually turned off. You should have familiarity with how a multimeter works to handle this task.
Instructions
Testing a Power Switch
1. Power down the computer and disconnect the power cord.
2. Open the cover and remove the lead that connects the power switch to the motherboard.
3. Insert the positive lead of the multimeter into one side of the connector and insert the negative lead into the other side of the connector. Be careful not to touch the two leads together.
4. Set the multimeter to the resistance (Ohms) measurement at the lowest setting.
5. Press the button and hold it for about three seconds. Watch the indicator on the multimeter to see if a change is noticed in the resistance.
6. Replace the switch with another one if the switch does not register a closed circuit when pressed.
Test the Motherboard Power Leads
7. Connect power to the power supply.
8. Small gold header pins connect the motherboard to the power switch.
Align a small metal screwdriver tip to touch both of the small header pins on the motherboard that connect to the power switch lead.
9. Touch both of the header pins simultaneously with the tip of the screwdriver carefully for about one second. If the computer turns on as if the power switch had been depressed, the computer power circuit is working correctly.
Tags: power switch, header pins, computer power, power switch, side connector