Paul,

These things can happen, if you flash up the BIOS and don't reset the CMOS
table and do the settings from scratch

I myself have not done that (reflashing the BIOS)*, but I can ofcourse not
say anything about the previous owner.

*I once trashed a motherboard because I tried to make a backup of the BIOS
first before flashing a new version onto it. And to add insult to injury, I
already had fixed the problem (the secondary drive being told to go to sleep
after just a few seconds) with a small program - but wanted to do it the
official way... :-(

if it's been blown away and the checksums fail.

I would expect that even if the CMOS checksum would not fail, a simple
sanity-check of the available data would also invalidating the contents
(assuming data gets shuffeled around and/or added).

The CMOS has documented areas, and undocumented areas.

Not really, but I take it you are referring to (in the old days) the
date/time related hardware in the first 14 bytes of the CMOS address space..

And because the developers weren't required
to "register" their usage anywhere, occasionally
there would be surprises ("undesired interactions").

AFAIK CMOS space is off-limits for anything else than the BIOS. But it
could happen ofcourse (though you would need to go low-level, as an OS as
Windows does not allow a user (of any level) to directly touch it).

There would be a bit of a problem with it though: if such a program would
try to use it for its own purposes it would alter some data, but not update
the checksum (it would not even know where it is stored nor how its
calculated), causing the 'puter to balk the next time its started.

In other words, as far as I can tell that scenario isn't all that likely.
Still possible ofcourse, just not likely.

Regards,
Rudy Wieser