This! Try this! Don't go taking your computer apart until you try this. It's great advice.

thanks! nice idea, i'll try it

Not really. Distros usually build the same software slightly differently. If the bug is in a piece of software used by all distros such as the Linux kernel, it won't make a difference.

thanks for your input but it looks different. I mean when I power it off with the button, then it is possible to boot without issues. Also it doesn't freeze randomly. It freezes only if it plays videos. Now it is 10 days on uninterrupted since I stopped playing videos.

Had issue with my storage recently, and the symptom was similar to what OP described. Syslog didn't reveal anything, as the root filesystem was read only, so troubleshooting it was hard. Coincidentally I needed a newer kernel, and after the upgrade the problem disappeared.

good idea about the PSU. I hadn't thought of that. The PSU is not any high-performance/high-quality and is already 5 years old. Being unable to provide the required voltage may be a possibility if we accept that the performance degrades in time. (Was working without issues for 5 years in the same PC configuration).

I think I'll try by first removing the extra HDDs so reducing the load and check again. Thanks for your input

PSU is the last thing we check but is usually the first to fail under load if it is old or cheap. Try reducing the load on it like not using ur GPU, HDDs or any other peripheral that is unnecessary.

Next check ur RAM, that too can give random errors under load.

This is the most likely issue. To add - test 3-4 passes of Memtest86+. The first pass is shorter and meant for finding egregious RAM problems. It can fail on subsequent full passes. I had my RAM fail on 3rd of 4th pass which passed the 1st. It could even be caused by incompatibility of the size of RAM with the platform. For example in my case AMD supported 2x 8GB sticks of this RAM with no issues. Insert 4x 8GB and it starts producing errors even if each individual stick passes with flying colors.

Seconded. I'd been having issues (random freezes, crashes) for a while but I had attributed then to a lack of RAM. So I bought some more RAM at some point and ran memtest on all RAM together and saw errors. Those bastards, they sold me dodgy RAM, right? Tested the new sticks individually, they were clean. Turns out I had a bad 64kb area on one of my old sticks.

You can tell the kernel to not use the bad area btw if it's all in one place, so don't necessarily rush out to replace the bad stick.

i will try it but I'm quite confident that it will be unresponsive/not reachable since if the kernel was listening it would respond to the alt + PrntScr + REISUB by unmounting the drives and I would see it when I examine the logs afterwards

mostly on youtube, usually at 720p30fps. I think if I go to 60fps it crashes even faster. Also I've tried watching on freetube and on firefox + mpv, but it can crash in all combinations

Why do you suspect gfx card?

because it happens only on video. Also if it is an 60fps video I start hearing the fans spinning like mad

What happens if you use a different video player, or play different videos ie different codecs?

haven't tried specific codecs. Usually it is youtube videos but makes no difference if I play them on firefox, on chromium, or even on opening them on MPV

Do you have an onboard gfx card you can use instead to test?

yes, there is one. Good idea.

but will I see anything more than what I see in /var/log ? I have checked all possible logs.. Or was your suggestion just for a better way to check the logs in general?

sorry if it is trivial but how do I check it?