I would ask you to short the power pins on the JFP front panel header on the motherboard but I'm not familar with the pinouts, use your motherboard user manual to located the connector pins for the power button for your computer case.
You can short those two pins for power button to test if you have a faulty power button or not.
If it still does not turn on then I'm leaning either towards faulty motherboard or power supply.
Power supply can be tested using the paper clip test but everything connected to the power supply must be disconnected before doing the paperclip test.
Power Supply Paperclip Test explained here:
https://www.evga.com/support/faq/afmviewfaq.aspx?faqid=59582