Extremely long story short.

I couldn't get the darn system (with all brand new parts) to boot at all for a long time. After a ridiculous amount of troubleshooting, I finally "fixed" it, or so I believed. For some insane reason the fix was mounting my GPU horizontally as opposed to vertically (removing my riser cable in the process). That solved it...

But a few days later I realized I can only boot if the system is off. If I try to restart the computer with the button in the Windows start menu or the reset button on my case, it fails every time. 5 beeps from the post speaker thing, which is a GPU issue.

Now I don't know what to do. Everything works perfectly right now, except I can't restart and I'm scared to mount vertically and have it start bugging out again (I bought a new riser, still in the box).

Also, I tried a different GPU (2060) I have with the same riser cable and same motherboard and it still failed. I thought that indicated an issue with the riser cable but now I'm thinking it's the board.

RMA or no? I would just accept things but the inability to restart makes it impossible to update Windows. And it's screaming at me.

Some specs:
Z690 Classified
13700KF
7900XT
1200W PSU and more than enough storage
custom loop

thanks

Definitely turn fast boot off.

Also, I had a somewhat similar problem (as part of another issue) wherethe system would fail to boot the first time, but needed a reboot to come back up. It turned out I had the cpu block on too tight. It's a water block for a custom loop and with no springs or specific stopping point, it must have been uneven or too tight to where it was bowing the motherboard. This can cause all sorts of issues, mine was usually giving a 7F error I think.