i dno if it was the psu, cause yesterday someone said p55-ud3 motherboard doesnt show signal if u havnt got ram in 2-4 and then i tried with 1 cause i was told to still no go yesterday, today tried with new psu and 1 stick and still didnt work n i got pissed off n started screaming over the phone like a little bitch to some fob that sold me the gfx card cos i thought it was faulty then i kept playing with ram combos and now it works in 2 & 4 even though was first way i tried it guess was psu lacking power