Asus M2N-SLI Deluxe Motherboard Won't Post After BIOS Update

I have an old Asus AMD AM2+ compatible motherboard that I'm using as the basis for a headless server for web hosting, automated backups, Bittorrent seeding, and a bitcoin node.  To Asus' credit, they're still supporting the thing with documentation and software downloads all of these years later.

As part of the server conversion, I picked up a bunch of off-brand DDR2 RAM on Ebay—it identifies itself as "Kingston Shenzhen" or some nonsense in memtest86—that turned out to be of the questionably-compatible high-density variety.  After mixing every possible combination of low-density and high-density RAM, I found that the this motherboard will happily take high-density RAM as long as only two or three of the four available RAM slots are populated.  It didn't matter if the third and fourth sticks were a matched pair of low-density RAM, the thing would freeze during the power-on self test (POST).  Sometimes you get what you pay for.

"Upgrading the BIOS" (basic input/output system) is a sort of can't-hurt-might-help black magic proposed on forums for curing every possible computer problem.  There is no reason to think it should help except in extremely specific situations, and if something goes wrong with the BIOS "flash" write operation your hardware is now a very advanced paperweight.  The risk just isn't worth flashing a new BIOS for no reason.

...but inevitably, over the hundreds of computers I've worked on, there was that one damn time when it inexplicably fixed the problem.  I really wanted to put some more RAM in this server, so I downloaded the newest version and rolled the dice.

working on this same machine shortly after I acquired it, back in November of 2012!