bad sector wrote:

Having 'increasing' probs with my 8-core AMD destktop.
The board is an asus-xhair-IV
/
No, it's "Crosshair" --- but which model is unspecified.

If you want to severely narrow down the responses to only those that
have this product to know you meant crosshair instead of x then don't
use abbreviations that would be uncertain to other users. In order for
other users (not of this particular motherboard) to be able to lookup
the product to know what it is to help you, don't make them guess as to
what you have.

From what I found in searches, the product's name could be:

ASUS Crosshair IV Formula
or
ASUS Crosshair IV Extreme

Didn't know which to pick, so I first picked the Formula product. That
was introduced around April 2010. Then I checked on the Extreme model
which looks like it came out around November 2010. From forum posts,
looks like both were discontinued around 2014 (replaced by Rampage).
You didn't say how old is whichever one that you have. At 10 years old,
that is way too long for the CMOS battery. Even at 6 years, CMOS
batteries go weak or die by then. I replace mine about every 3-4 years.

During boot, the settings from the battery-powered CMOS table are used,
if usable, but if corrupt then the BIOS will try to retrieve the
defaults stored in the EEPROM chip(s).

It's a cheap troubleshooting step for an old computer exhibiting boot
problems: buy a CR-2032 coin cell battery, and replace the old and
likely dead one in the computer on the motherboard. Since both the
Formula and Extreme models are motherboards for desktop PCs, replacing
the CMOS battery is easy. Laptops are a bitch.

Boot often doesn't even begin and pops the subject
error message which includes "or F.. to load defaults"
and words of this nature.

The CMOS battery is probably dead. It cannot maintain the contents of
the CMOS table, so the contents of that table are corrupt or invalid
forcing the BIOS to load the defaults from the EEPROMs. Replace the
CMOS battery, reset the BIOS (use a jumper to short the 2-pin header on
the motherboard) to ensure the defaults get loaded into the CMOS table,
and retest.

I would just like some ballpark hunches to start with, what
do symptoms like this suggest? Mobo, rack, bios?

Most likely needs a new CR-2032 battery. I get a bunch of them at a
time for cheap at eBay, but make sure you aren't buying counterfeits
there. Ask the seller if the pic they show in their auction is of the
product, or a stock photo. If a pic of the actual product for sale,
often the packaging will indicate authentic or counterfeit (and there
are sites showing you pics of authentic vs counterfeit packaging). I
have lots of devices using the CR-2032 batteries, so I buy a bunch to
replace them all or have spares on hand when they die off. At Walmart,
it'll cost more (~$5), but you only need the 1 for the mobo for another
4 to 6 years before needing to replace it again. I usually stick with
Sony for the coin cell batteries.