Revert the BIOS back to an earlier version that 'did' work. Newer doesn't mean 'Better' and especially not with the BIOS.
ONLY use ASUS EZ Flash 2 - http://www.tomshardware.com/forum/289507-30-what-flash
Clearing CMOS, most folks don't do it correctly. Unplug the PSU for ~5 minutes for the PSU to discharge then using the 'Jumper' method and leave the Jumper for a minimum of 5 seconds (longer if fine less isn't); watch -> http://www.youtube.com/watch?v=rdHH9KrceR0
/edit - I read what you said and IF the BIOS updated correctly it should allow a downgrade if the BIOS is for your MOBO and from ASUS's site.