first off check the mb ram guild and the ram you have. you may have to call or email the ram vendor to see if the ram you have is a replacement or new model that replaced one on the mb qal list. i have a 16g set of ram from gskill and a new asus z77 mb and it will only boot with two dimms. if i put three or 4 in the mb ram led will go red. i would swap one dimm and run memtest on two dimm at a time to see if one of the dimms are bad.