BB, may I ask a couple of obvious questions?
Firstly, can you boot from a simple DOS Boot Floppy?
Second, if the answer to the first is "yes", can you interrupt the boot to got to BIOS setup?
Mostly, BIOSs allow you to go to Manufacturers defaults in cases like this. (F9 or F10 usually).
It does sound somewhat extreme to condemn the poor old MB to death because of a glitch in a BIOS update.