Having figuratively smashed my forehead against the motherboard for the last day, I can summarize this problem more succinctly:
When I power on my computer, I see the message
Asmedia 106X SATA Controller Ver 0.90 IDE Mode
Using PCIE Gen 2
Can't find any device.
* The motherboard gets to that point, implying that it POSTs
* It will not print any messages regarding the BIOS
* It will it enter BIOS under any keystroke (F2, DEL, others)
* Once it showed "B4" in the lower-right corner and flickered to "99" before the error message appeared
Thus the question is, what kind of problem could cause the motherboard to print that message, yet refuse further input, and refuse access to the BIOS? Could there be any conclusion other than bad motherboard?