1. Please make sure the power cord is connected securely to the power supply and the power outlet. Ensure the power supply switch is in the ON position (The on position is in the picture below).
2. Please double check that the pw sw connector is properly seated on power sw pins of the motherboard.
3. Please pull out pw sw connector, and short the pw sw pins on the motherboard by using a screwdriver. If you can not boot up the pc, then there could be an issue with the motherboard or PSU. If it powers up, then there could be an issue with the power button module or pw sw pins on the motherboard.
NOTE: Shorting the wrong pins can damage components. If you are not sure if you have everything plugged into the right places, please get professional assistance.