Hi canuck,
I was in this position last year. Mine was a necessary flash to gain support for ivybridge CPU.
Had full system back up
Had back up of current BIOS on USB
System connected to UPS
Flashed using DOS based utility
Update reported successful
Then boot loop
No POST
No BIOS
No recovery
No external boot device would detect
Couldn't even boot from the MB CD which is what Asus calls crash-free recovery when a "good" BIOS flash goes wrong
Like you I tried it all, your list brings back such horrible memories. Something so simple and routine fails. Enough of my story.
autotechs instructions are recommended <<<
Based on your description/troubleshooting steps, it sounds like the 1st chip is hosed. (if removing the MB battery with the power disconnected doesn't resolve). Sadly the Z68, Z77 and X79 MBs share the same flaws when the boot block recovery portion of the BIOS image becomes corrupt. At that point, a single chip BIOS is finished. Board is a brick. With mine, I considered a hot swap reflash, but the replacement was $18 and I had already been up like 18hrs trying to resolve. Asus BIOS chips aren't soldered to the board... but there is only one.
Hence, I'm done with those guys after 13 yrs.
So you've got to get that second BIOS chip to activate if there is any hope of resurrecting your system.
FYI, the BIOS chips are 64mb, 8pin PDIP 300mil. Apprehension aside, you don't have much more to lose. If you don't get the second chip working, the primary chip will have to be removed, reflashed and re-soldered to the board. I hope you can recover