Just wanted to share my experience in case it helps someone dealing with the same issue.
I recently installed macOS Sequoia on my PC, mostly out of curiosity. I don't really need macOS since I use Windows for work and gaming, but I wanted to see if I could get it running on my hardware.
My setup:
- ASUS PRIME B650M-A AX II
- AMD Ryzen 9 7900X
- NVIDIA 5070 12GB
- 32GB DDR5 RAM
- macOS Sequoia 15.8.1
- OpenCore 1.0.9
- NullMoth 1.15.0
I managed to get macOS running with both monitors connected to the NVIDIA 5070. Everything seemed to be working fine, at least during the time I spent testing it.
Then yesterday, when I came back home and turned on my PC, I got absolutely no display. Not even the ASUS logo or BIOS screen. The fans were spinning, but the power LED kept blinking slowly, about once every two seconds.
At first I suspected the GPU, so I completely removed the NVIDIA 5070 and connected my monitor directly to the motherboard, using the Ryzen's integrated graphics. Still no display.
I tried reseating the RAM, waiting several minutes for DDR5 memory training, and clearing CMOS through the CLRTC pins. None of that worked.
I was starting to think my motherboard had died.
Luckily, my ASUS motherboard has a BIOS FlashBack button, so I downloaded BIOS version 3881, put the renamed CAP file on a FAT32 USB drive, and reflashed the BIOS without needing to boot the PC.
And that fixed it.
The ASUS logo appeared again, I was able to enter the BIOS, and Windows booted normally. I reinstalled the NVIDIA 5070 and everything is working fine now.
After this happened, I found a couple of threads here describing very similar problems with AM5 motherboards and Hackintosh/NullMoth. Apparently, there have also been concerns about UEFI variable writes on these systems.
I can't prove that NullMoth or OpenCore caused my issue, but the similarities are hard to ignore. I also can't tell whether the firmware was actually corrupted or if reflashing it simply reset something that clearing CMOS couldn't fix.
Anyway, I decided to stop experimenting with Hackintosh for now. It was fun getting macOS to run on this hardware, but it's not worth risking the PC I use for work.
TL;DR: My ASUS B650 motherboard suddenly stopped POSTing after I had been using Hackintosh with NullMoth. Clearing CMOS and removing the GPU didn't help. Reflashing the BIOS using ASUS BIOS FlashBack brought it back to life.
If you're having a similar issue with an AM5 motherboard, don't assume it's dead before trying BIOS FlashBack (or your manufacturer's equivalent), if your board supports it.
Hope this helps someone.