After running Windows Update, one of the updates was for a VIA device driver for the primary IDE controller. I went ahead and let it install. On rebooting, I wound up in a BSOD loop. The only way past was to select "boot from your last working configuration." So I'm thinking that accepting that driver is a bad idea.
Yep, got exactly the same problem here. Going back to the last working configuration seems to have rescued it fortunately!