[Post-Install] Random hard lockups, trying to understand how to diagnose.

[ansel]

Hi all, I've had persistent issues with my machine hard locking up- unable to provide any input to the system, have to hard reboot. It occurs randomly with no pattern in timing or applications or system usage, and happened sporadically since I switched from windows 10 to Kubuntu in fall of 2025. There's seemingly no trace of the crash or any errors in my logs, from what I can tell.
I'm just a casual/hobbyist user, and I have an okay enough understanding to get by. I am unsure where else to go with finding the cause of the issue. I'm aware of the common ryzen processor issues relating to c-states, but the fixes have not resolved the issue.

Here are my specs:

Operating System: Kubuntu 25.10
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.17.0
Qt Version: 6.9.2
Kernel Version: 6.17.0-8-generic (64-bit)
Graphics Platform: Wayland

Processors: 12 × AMD Ryzen 5 3600 6-Core Processor
Memory: 32 GiB of RAM (2x 16GB DDR4)
Graphics Processor: NVIDIA GeForce GTX 960
PNY CS900 240GB SSD (OS Drive)
WDC WDS 500G2B0A-00SM50 (Home Drive)


Things I have tried:

Swapping graphics cards, checking cable connections: no change.
memory test, 2.5 hours: all pass.
disabling c-state control in BIOS: no change.
disabling c6 c-state via ZenStates: no change.

It's a bit hard to test since I just have to make a change and wait to see if the crashes continue, which could be hours or days between. Anyway, thank you in advance for any guidance.

[jlittle]

Power supply? You don't mention it, but if it's a similar age as the GTX 960, it's getting old. My desktop's nearly 10 year old PSU failed recently, though it just shut off rather than locking up.