Question ASUS motherboard won't boot into Windows, not even into USB after BIOS update

[Cctcat70]

Hello everyone,
I have this problem that my PC just won't boot into Windows 10 from NVMe drive, not from USB to Windows Installer, not from SATA DVD drive and not from a SSD that has Linux on it - right away after updating my BIOS.

Firstly, there was another problem before this problem which I am not sure it might be 100% linked to it. My PC has worked flawlessly until some random unexpected restarts have started happening. (This issue also happened more than a year ago few times, but went away.) The screen went dark, the motherboard speaker beeped, ASUS logo has showed up and the PC booted as usual. Event Viewer has showed that Memory is an issue.
I thought a BIOS flash might fix that problem so I tried that.

So after updating the BIOS to the newest version, my PC just won't boot into Windows from my NVMe drive, and into everything else I stated at the begginning of this post. It initially kept being frozen on ASUS logo, with no loading dots (still sometimes is). When I tried to boot Ubuntu from another SSD, the PC just restarted back to the ASUS screen. After trying to boot Windows 10 for few tries, it managed to show an error saying that Boot Configuration Data doesn't contain valid info for an OS. This error might be caused by me executing some BCD repair commands in Windows Recovery Environment running from USB before I updated the bios but the PC has started normally after running the commands at that time.

Booting Windows Installer from USB now does not work. It either is stuck on ASUS logo, on a BSOD with and sometimes without a QR code and error, and sometimes it gets stuck on plain blue screen with no text.

BIOS works. I can access it. I have disconnected other drives, tried to also disconnect the NVMe drive when trying USB boot, do a CMOS reset (the time and settings are reset, but favorite settings in advance mode are still there. I have also did reset to default settings, from the screen but when I looked at boot config menu, it showed disconnected drives as boot drives), tried to change CSM, TPM, secure boot settings, tried downgrading, but same issues persist.
I have also checked and reseated the CPU, it does not appear to have any damage, Disconnected extra wires for front panel, power & hdd light and audio, tried switching RAMs with older ones and same problem happens so the RAMs should be fine.

My specs are:
Mobo: Asus Prime B450m-k
GPU: Msi Geforce GTX 1060 6GB
CPU: AMD Ryzen 5 1600X running at base freq
NVMe: Samsung 980 Pro
PSU: BeQuiet! 550W

The PC with current mobo, gpu, cpu, disks is 4 years old but runs on much older PSU.

I really don't know what could cause this. I have seen other posts and they say that the CPU might be issue but it has worked with no problems.

Any help would be very appreciated. Thank you in advance.

 

[Lutfij]

The PC with current mobo, gpu, cpu, disks is 4 years old but runs on much older PSU.
How old is the PSU in your build?

If you're clearing your CMOS, you're advised to disconnect from the wall and display, then remove CMOS battery, press and hold down power button for 30 secs then replace the battery after 30 mins.

 

[Cctcat70]

PSU is 10+ years old.
While clearing CMOS I did those steps, I also left the battery out for more than an hour.

 

[Cctcat70]

So after all, the PC randomly shutting itself actually was a sign that the CPU was dying, and when trying to boot it, it was already dead. Swapped with a new CPU, the PC now works. Don't know what could cause the CPU to die though.