And then it spun up a disk, and went back to acting normally.
And a little message box popped up, saying, "You've just lost a disk."
Slightly perturbed, I went into the Disk Manager utility to investigate, and discovered that that wasn't entirely the extent of it; both disks attached to IDE0 had little yellow exclamation-point icons and "unreachable" notations, and the partitions on them were listed as "Failed Mirror". And it occurred to me that there was perhaps some pleasant luck in that all of my software RAID-0 arrays were set up across two controllers.
Suddenly, the idea of the system dealing with this with merely a half-minute of inaccessable filesystem and five seconds of minor lockup didn't seem like an unreasonable thing at all.
Anyhow, it seemed like it was probably not a good state to be continuing to run the system in, given the sudden lack of backups of a lot of my data and the sudden evidence of why backups are useful, so I shut it down and power-cycled it to see if that helped. Which just provided evidence that the problem was repeatable, and a reminder that the BIOS kind of needed to read one of those disks to get to a boot sector. So it's currently not rebooting.
Still, I'm rather impressed at how well Windows dealt with that.
And I guess that means that it's really time to go ahead with the motherboard upgrade I've been meaning to get around to doing for about a year. Sigh; I really wasn't looking forward to all the reinstalls that I need to do for that.
(Hmm. Okay, maybe I'm still a little annoyed at Windows, given that I've been swapping a FreeBSD install around between several different computers and it's been perfectly happy with the hardware changed.)
Anyhow, internet access is likely to be a little spotty for a while until I get a chance to do something to deal with this. I'm currently using my laptop with a Google wifi connection, but those tend to be flaky when the sun's up.