Question 2 Dead Motherboards, 1 GPU

Jul 29, 2021
Okay so I've prolly had / built 20+ rigs over the years fairly knowledge able about computers ect. recently I purchased a eBay "for parts or not working cyberpower PC with a 9700k / RTX2070 Super in it. after hooking it all up, absolutely nothing happens when when the power button was pushed. jumped out the pins, ect, nothing. I have 2 other Z390 systems so i was able to test out the CPU/GPU/RAM/PSU/SSD everything. All was fine leading me to believe there was an issue with the motherboard. so that being said, I took out the GPU and put it in my driving sim rig as an upgrade. drove for one hour on day one, zero issues. day 2 I decided to stream some sim racing. do 20 mins of practice, qualifying, 7/10 laps into the race, boom, my VR goes black, PC is off. exact same symptom as the PC i just bought. everything works, but the motherboard appears to be dead. does anyone have any guesses to what is happening or a fix once my new motherboard(s) come in. 1000W EVGA 80 Gold PSU. i cant imagine its power delivery. Did not use pigtailed GPU power, ran 2 separate lines. The only thing the 2 systems had in common was the GPU... Any thoughts. and also. Both motherboards RGB Lights will light up when plugged in, but thats the only thing that appears to work on them.
Any help is appreciated