did you rename the bios correctly? it needs to be exactly EVGAA577.bin and placed at the root directory
plug your usb into the flash header, and hold the reset button until the rotating animation starts, and leave it the computer should start once it done flashing.
also the flashing process only flashes one bios at a time there should be zero reason the second bios wont work if the first failed to flash.
if all else fails use the flash the original bios from the supplied usb driver disk