Z790 Steel Legend not booting

I rebuilt my system in April around a ASRock Z790 STEEL LEGEND. Everything worked on first try, but I left out the graphics card since I wasn't using it.

I recently tried to install the graphics card. It didn't work. Hitting the power made the LEDs on the card flash, the DRAM led on the board stay on, and the system never booted.

Checking everything was correct, I noticed I accidentally had the 8-pin 12V CPU connector in ATX12V2. It was that way since April and never seemed to cause a problem. I moved it to ATX12V1 and the power switch does nothing. When the power is connected and the power supply is switched on, a lot of LEDs come on with the board. But hitting the power button does absolutely nothing visible or audible. Removing the case power switch connector and trying to turn on the board by shorting the LEDs with a screwdriver does nothing either. Moving the connector back to ATX12V2 doesn't change the behavior, and now I can't boot at all.

Is it possible I fried my board? Is there a fuse or breaker that can be reset? Could this be a bad power supply? I have a tester on order. Any other ideas?

Thank you for creating this thread for me.

I agree it is far more likely I ruined my board with an improperly connected PCI-E card than moving the 8-pin power headers.

I bought a brand new Corsair RM750e along with a tester. My old Rosewill PSU tests fine across everything. The new Corsair reads 13.4V on the -12V line, but is otherwise fine across everything. The system behaves exactly the same with either power supply.

What is the best way to know if the motherboard is bad?

What are the minimum connections I need to boot to POST, or at least start the process? I have 1 RAM module, CPU, both ATX12V1 and ATX12V2 (with the new PSU) and ATXPWR1. Is the CPU fan required? Obviously I don't want to run a long time without it, but I am trying to minimize what is connected. I've tried either way, nothing works.

Any other ideas or suggestions?