Computer not posting mobo compatibility issues, bios update

Hello,
just finished a new build and the mobo wont post it comes up with an AF Qcode (p9x79pro mobo) i tested the ram and its good, i did some research and people have been having this problem with this cpu mobo combo (i7 3820 cpu) im trying to flash the bios useing the .cap file with the usb flashback but the best i can do is get it to flash 3 seconds and stable which means something is wrong with the file or something but ive checked it a BILLION times and yes the usb is formatted to fat32 etc i have also cleared the cmos inbetween flash attempts, honestly i am out of ideas ;-;