Since there are many discussions about this issue but most are now closed, I wanted to share the solution that worked in my case.
I recently encountered the same problem with my ROG Strix Z790-F, where the BIOS Flashback LED kept blinking, and the power button wouldn't work properly. After some troubleshooting, I found that the issue was caused by debris in the USB ports near the blinking button and on the I/O panel itself.
My motherboard is installed in a 90-degree rotated position inside the case, with all I/O ports facing upward. The night before the issue appeared, I had been cleaning my workspace, where I often work on DIY electronics projects and cut micro cables for soldering. I also noticed that my PC case had no protective mesh on top, which likely allowed dust, plastic fragments, or other small debris to fall onto the I/O panel, possibly interfering with the contacts.
I simply blew on the ports with my mouth, and then I used scissors to pull out a small piece of plastic that was deeply stuck in one of the USB ports. Additionally, in one of the Type-C ports, there was a thread—or maybe a tiny strand from a multi-core cable. After removing all this unexpected garbage and giving the ports a good treatment, everything started working again, and the power button functioned normally.
So, if you're facing a similar problem, I recommend checking for dust, debris, or anything that might be stuck inside the USB ports or around the BIOS Flashback button.
Hope this helps
