GRUB go poof! BIOS spontaneously reset?

The following problem is solved... But it's a wierd one and I'm
wondering if it will repeat.

My wife's little PII 400/100. RH9 install. Was working fine this
morning, then she heard a noise "like the neighbors hammering nails in
the wall but it was in the computer" (I wasn't there). Then her network
connectivity stopped. Standard M$ programmed response, she rebooted.
On reboot, she didn't even get GRUB, just a black screen with blinking
cursor where and when GRUB should have been. I tried a few times, same
black screen. Tried Knoppix: it didn't see my primary master!
Massaged the IDE connectors and power connectors, retried Knoppix, ahh
the partitions are back. Did an fsck -c -f on all, clean. But
rebooting still gave me a black screen. Rescue disk RH9, tried both
reconfig and reinstall of both GRUB and LILO, same black screen. Wiped
the partitions except /home and installed Fedora. Same black screen.

Then I noticed something in the BIOS that I never noticed before: you
can configure the order in which the "hard drives" are accessed to find
an MBR. I don't mean 1) removable 2) CDR 3) HD 4) net, I mean inside
option 3, there are three more options, which was configured 1) Bootable
add-in cards 2) Maxtor (SM) 3) Maxtor (PM). I don't have any bootable
cards (that I know of?). Secondary Master is the wrong HD on this
system, the MBR is on the Primary Master. So I switched to exactly the
reverse (PM,SM,bootable), and wow, GRUB came back!

Okay... So how can this be analyzed? Did the RH install work on the
old (bootable,SM,PM) configuration then suddenly stop working? Or was
it set to PM,SM,bootable and somehow reset? Because there was some
physical noise, maybe some physical problem caused the BIOS to reset?
Maybe if a drive is physically yanked, the BIOS setting automatically
does some corrections, then did the wrong correction back when the HD
was restored? Anyone else have this kind of wierdness?

--Alexander