Computer shuts off arbitrarily

Hi,

I have a very annoying problem: my working computer shuts off nearly every day at least once, all of a sudden. No blue screen, no crash report, nothing - just completely shut off and I have to press the power on button to restart it.

It is a Windows machine, if that is important.

I have run a memory test already, but nothing was found. I don't run any big stuff, so it is very unlikely that this is an overheating issue. I have enough fans and they work, so I doubt that this could be an issue.

Do you have an idea or suggestion what I can check or how I can narrow down the problem?

Thanks and best regards