Have you tried resetting the BIOS to the default setting by clearing the CMOS.
Instructions are on pages 45 & 46 of the Mobo Manual.
If you need the BIOS Flashing files thay are at
ASUS they should only be used if you are 100% confident you know what you are doing.
Most Flashing tools need to be added to a bootable floppy disk, these can be made in Windows.
Before Flashing the BIOS make sure you read and understand the instructions in the Motherboard Manual !!