Help have just put 2gether my first pc "BUT" power is getting through as all fan's are spining and light's on but my screen comes up with no video output but i know it's not the screen because it's fine with my old pc??? so cant see bios or any thing,My 24 pin main power lead is in two picece's one of twenty pin's and one of 4pin's do i need to put both in aswell?