I had a 3 years old Asus TUF Gaming B550M-Plus with a AMD Ryzen 5 and a Nvidia GeForce GTX960 in a dual boot Windows 11 Pro / Ubuntu 22.04 with a dual monitor primary DisplayPort and secondary monitor HDMI.
It died after several weeks of almost no symptoms, except for a weary system clock that could not update during shutdown, hibernation or suspension. I thought that it was a clock battery problem, but I removed and tested, and it was full.
I boot with no other issues but, next morning, dead PC with no lights at all.
I did the usual investigation, all parts were OK, except the motherboard. So, I ordered and got the exact same motherboard, of course with a different revision and BIOS after 3 years, but side by side all components and boxes are identical.
I installed and it failed in POST because of video (light and beep pattern); the strange thing is that when I remove the DisplayPort cable it POST normally and I could enter UEFI, reactivate Windows, etc.
Every time that I connect the DisplayPort cable I cannot boot. And when I connect it after POST, I can use Windows normally with the original DP/HDMI two monitors, but restarting PC, the same error...
I installed the GTX960 and the same DisplayPort cable in the other PC, no errors at all, but it is an ASUS Prime B560.
Investigating things in my PC, I know that the last UEFI version that I updated the dead motherboard with was a 2021 version; this motherboard is from a slightly different revision and came with a 2022 UEFI version, that I already updated to last, dated October 2023.
Any directions?
It is working; but Ican only boot with the DP cable disconnected and connecting it seconds after...
I did some search and did not find an answer.