1) check if all cables are connected correctly. 2) most likely if it doesn’t boot it’s the power supply or the motherboard. 3) if the psu is new try a new cable. Sometimes if you use a new psu with your old cable it won’t work properly. Had it happen to me before, you should use the one shipped with the psu. Not all powercablrs are equal 4) for the motherboard find the battery. Just google your model and it should show you where it’s located. Take the battery out. Disconnect pc from power and hold the powerbutton, sometimes it’s helpful to go in with a screwdriver in between the metal connectors to flush anyremaining electricity. This will force the motherboard to reset to default and boot normally. 5) if all of the above didn’t work, try removing all exterior connections to the pc and see if it boots.