Crosshair VIII Hero X570 / Ryzen 5950X not loading Windows or Linux - freezing at OS load screen

[ErikTechie]

My custom gaming PC "died" today for some unknown reason. It simply would not boot into Windows 10 nor Linux Mint. The operating systems would not boot; the computer would freeze with the spinning circle (Windows) or black screen (Linux). It would not reach the login screen. I spent hours trying many troubleshooting steps (explained later below).  This issue began occuring after Windows froze hard during a large file copy from one drive to another.

The fix? Choose "water-cooled OC preset" from the ASUS BIOS "load optimized defaults" option in the "exit" tab. I'm still unsure how that fixed the issue, but the system has been running for hours without issue (albeit at faster CPU clocks).  Can anyone explain this?

Troubleshooting:
- Ensured no cabling came loose.
- Disconnected cabling and sprayed out the case/fans with compressed air (it was very dusty).
- Disabled SATA in BIOS, enabling only the NVMe boot drive (Windows).
- Unplugged the SATA cables from the hard drives (they are just extra storage drives).
- Swapped the video card with a working spare (GTX 1080 Ti).
- Reseated the RAM sticks, and ensured they and the slots were dust-free.
- Ensured the fan speeds were at full RPM and CPU/motherboard temperatures within acceptable range (55 deg. C shown in BIOS).
- Set memory clock speed down to the default 2133 MHz., disabling Asus's DOCP profile (which uses XMP settings).
- Bumped the SOC voltage to 1.25v, up from 0.9v.
- Reset CMOS settings by removing CMOS battery for a few minutes, then reinstalling.
- Updated BIOS firmware to 4006 (the next version up from my existing 4004), and then again later to the latest 5002, using EZFlash/USB drive in BIOS.
- Running MemTest86 using a bootable USB drive, for hours. 0 errors found when running at my original settings of 3200 MHz.
- Tried booting using a Linux Mint liveboot USB drive, which the computer loads to the boot screen, but stalls when the kernel/drivers are loading (just like Windows).
- Ensured CSM was disabled for USB booting (only UEFI mode). But also tried with CSM enabled. No difference.

[ErikTechie]

Update:

tldr; If no OS won't boot properly, and all other troubleshooting fails, reset the CMOS settings. This can be done by loading a preset in BIOS, amongst other ways.

Computer has been running fine for nearly 2 weeks running 24/7. The watercooled OC preset set very aggressive CPU speed/thermal settings in BIOS causing reboots at 80 deg. C so I had to change those to more conservative settings. Processor limits to ~70 deg. C now and averaging 4.2 GHz. all-core. Memory set back to original DOCP/XMP 3200 MHz. settings.

What I believe caused the issue was somehow the CMOS got corrupted (possibly from storms/power issues), and using the BIOS to load any preset effectively resets it. Removing/reinstalling the CMOS battery apparently doesn't do this.