My desktop had developed a strange habit this morning: shortly after starting up and logging in, it shutdown very suddenly. There was a mechanical noise like a relay opening, the fan spun down, though the power light remained on. I restarted and the same thing happened again. It takes anywhere from seconds to minutes for this to happen. When I went into the BIOS settings I got a message saying that they had been reset. The most perplexing part is that I don't think I changed anything recently that could explain this.
Clearly I'm not hoping that someone will diagnose the problem from these paltry details. But I'm wondering how I can go about collecting more information about the shutdown. I'm running Debian Buster.
I'm really quite clueless here - what (if any) 'blackbox' recording do I have available after something like this?