Felicia has been behaving very well for about 6 weeks. Now I have just replaced 2x512 MB DIMM memory cards by 2x1 GB - accepted by BIOS but Felicia immediately refused to boot, going repeatedly into BusyBox.
I've complained about BusyBox before, and last July was advised by "ryawn" in the forum to edit the kernel line in /grub/boot/menulst replacing "quiet" by "all_generic_ide floppy=off irqpoll". That was successful in Elyssa, and up to now has not been required in Felicia.
Now I've done that in Felicia, without success. Greatly daring, I decided to edit the file /boot/grub/device.map which has been set since installation as: hd0 = sdb; hd1 = sdc; hd2 = sdd. Now it has the "sensible" setting - hd0 = sda; hd1 = sdb; hd2 = sdc. Of course I had to edit menu.lst correspondingly - in the kernel line root used to be sdb2; now it's sda2.
And with that, my system has successfully booted! Possibly the replacement of "quiet" may not have been necessary.
BTW - how do I edit these files in a non-booting system? I use Puppy Linux, which runs in RAM and is very versatile for such purposes. I think that tip came from Fred - thanks very much!
[Edit: 8 PM 4/3/09]
After I restored "Quiet" I was back to BusyBox, so I undid all my changes to the files in grub and again replaced Quiet as above - then I had a successful boot. I do find these changes puzzling.
[Second edit: 1:10 pm 6/3/09]
Now I've gone back to the original changes - Device map set to sda, sdb, sdc and menu.lst corresponding - and it boots successfully with the kernel line in menu.lst edited with "quiet" replaced as described above.