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 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 jumper.
NOTE: Wrong short could cause components damaged, please ensure that all steps are going well. If not, please ask professional IT expert for help.