I've had success in the past with the following:
1. remove any device attached to any USB port (except keyboard, if you have a USB keyboard). For this particular BIOS, attach the keyboard to one of the USB 3 ports (blue insulator) on the back panel.
2. Disconnect the power supply from the mains (pull the plug)
3. Hold the case power switch (or the power switch on the motherboard) closed for at least 30 sec
4. reconnect the power
5. proceed with the documented BIOS recovery technique of your choice. BIOS 53 has an apparent problem with the USB 2.0 ports (black or yellow insulator) so if you're loading the .BIO file from a USB flash storage device your best chance of success will come with using one of the USB 3.0 ports on the back plane.
Thanks for the tips, unfortunately it did not work, the motherboard is dead as a doornail. Another replacement on the way.
I've also observed that the BIOS is flaky as hell dealing with USB keyboards and mice. It often completely ignores my pressing F2 unless I tap it repeatedly for about 30 times during POST. I would definitely trade the visual BIOS for reliable USB detection during POST. I've tried every port and had the best luck with the front USB ports on my case, which plug into the motherboard's first USB pinout. But only if the mouse is not chained off the keyboard, and only if I'm not trying to use the KVM, which the DZ77GA completely ignores no matter which port I plug it into.
And to top it all off I'm now terrified of updating the BIOS unless I have a spare motherboard handy.