I having a hard time troubleshooting that one.

My old PC with a 7700k, Asus z270 TUF Mark 2, 2080TI is not posting. No fan spinning. Like if the power button was not even connected. When powered, I see a green blinking led on the board and a orange one as well.

1. I had another 850W power supply lying around. So I swapped it. Same result.
2. I swapped the C-mos battery with a new one I had. The older one was quite low (1.5V or so). No change. Cleared the CMOS, removed the battery, unplugged the power, cleared the CMOS again for 25s. Put the battery back. No change.
3. I removed the GPU. Same result.
4. I removed the RAM, one by one (got 2). Same result.
5. I then looked for defect on the motherboard and almost burnt myself when touching the southbridge. The leds were not blinking anymore, they were solid green and orange.

Got a few questions? Is the Mobo dead? Can I get the same mobo again (seems unavailable)? Can I even buy a LGA1151 mobo in 2023? If I buy a new one, do I keep my windows install? Or do I need to start over?

Thanks in advanced for the help.