I have done all the diagnostic steps and have verified a good PSU. Solid green light but no power flows, whether everything is plugged into the board or not.
How do I go about getting a replacement motherboard? I'd rather not start the pattern of buying a $2,000 computer every two years.
Sorry to hear the news. You can try contacting HP for direct mobo replacement and get a price. If they even have any extra stock. Most likely not. The other way. Buy a whole new mobo with OS and possibly new case. Then reuse rest of the parts.