Also try flash the BIOS again with USB again. Sometime it will work. And if you can't work it out, you have to contact gigabyte to see they will replace the BIOS chipset or MB for you.
Keep in mind your MB has only one BIOS chipset, if you screwed it up, you have to replace that BIOS chipset. If the MB has dual BIOS chipset, you will have chance to use the backup BIOS chipset.