if it just flashes it telling you there bad power or a dead short. start with pulling the gpu and all the ram but one dimm. if the mb still showing dead short. unplug the case fans and cables...check that the mb sitting on all the standoffs and the io shield not shorting the mb out. if it still shorted..pull the mb see if it start with just the ps outside the case. if the system still shows short. make sure the cpu cooler not on to tight and check for bent pins under the cpu and try another power supply. on testing the mb if the power good led is weak or blinking it a sign of a bad power supply.