You did flash the correct BIOS for the board? I know Gigabyte makes several variations of the same motherboard, with different hardware components, so flashing the wrong BIOS, even if it's the same chipset, could hose the board somehow.
Try clearing CMOS first.
Otherwise, the BIOS got hosed somehow. If you've got the Dual-BIOS feature with that board, follow the instructions in the motherboard manual on how to use the Dual-BIOS feature. Otherwise, get ahold of Gigabyte about a replacement chip or other means of getting a new BIOS.