Many thanks to all who have replied!
butre:
the mobo is an ASUS X99 Workstation, but I also have an ASUS gene (even older than the X99) that also has socketed bios. I haven't been shopping for new mobos in ages, but I was under the assumption that, for ASUS at least, socketed BIOS was kind of common.
suicidal orange:
I don't know. (I couldn't find a screaming nor a pulling-out-my-hair emoji, but those are exactly the emojis that I would have used had they been available). All H/W was bought NIB either at MicroCenter or else on Amazon (sold by Amazon only). Too, I have never over-clocked it and everything that I bought I had thoroughly vetted, myself, against the recommended H/W from the support pages for the MOBO. Too, this is like the 5th complete computer that I've put together - of course, I'm not a systems engineer or anything, but back when I put this together, I really, really took the time to do this properly.
As I've been researching this issue, I've heard suspicions that X99-chipset-mobo-vintages are more likely than others to have problems with their BIOS chips.
I did update the BIOS three times back in the first year that I bought it: successful flashes each time (b.c. there was a slight problem with USB handling).
That said, this system was purring like a kitten for five years right up to the day that it wasn't.
Also... system was entirely air-cooled (all Noctua) and I log temps and speeds over all cores for heavy workloads - I've never seen any unusual spikes that would even begin to suggest that I was running too hard or too hot.
LesleiAnn:
a. not an OEM system - totally DIY, so that's a plus: it's a hard copy of Windows 7 that I bought on disk back when you could do such a thing.
b. no RAIDed drives, so that's another plus.
All,
One more question for you, if you don't mind: what if my boot drive is NVMe (hint: it is, LOL).
Cheers & Thanks to all for your replies (this is almost like losing a pet - I swear I went through various stages of grief management when this box went down),
K