Hello,have acer m3100 desktop had vista 32bit,3gb memory 2 at 1gb,2 at 512gb ,upgraded to win 7 64 bit ultimate,did crucial memory scan says can hold 8gb pc5300,pulled 2 at 512 and replaced with 2 at 2 gb for 6gb total,now will not boot goes to safe mode sreen,memory is same make as 2gb left in what could be problem