I bet you were thinking Chuck and Larry, weren't you? Wrong guess :)
I now pronounce my main machine to be terminally ill, and practically deceased. While it was running rather stable last night with some extra cooling - thus strengthening my guess that some fan wasn't up to it's task anymore - today it shut down without any error and rebooted, twice. Sounds like something is seriously amiss, ain't it?
Anyway, I followed Hilda's "Zen Zen Zen" advice and flicked the power off, dropped a load of laundry in the washer and went to take a shower. No need to go crazy about something I saw coming. I managed to write a couple of CD's last night containing a bunch of things I'll need if I reinstall or move to another machine, and all (I think I got them all) my passwords are safely backed up as well, so till I have decided what to do with the old box, there is no need to stress about anything. Sure, access and reply to mail may be a bit slower, but all things considered, this ain't something that can't be resolved with some effort and focus.
Oh, because I can't stay away from privacy related topics, I'm pointing you to a complete set of instructions regarding preserving evidence on electronic devices to be followed by UK police officers at ACPO Guidelines for Computer Evidence (PDF format, 2.7MB). I do that not because I want you to know how to commit the perfect crime, but because it'll make you understand that traces are left everywhere and removing data may be practically impossible.