bought 2 Dell E172FPB computers both would not power on... I took them apart and went through them step by step removing the components trying to see what was wrong with them.... When i remove the ribbon cable that goes to the lcd screen the back light comes on and is nice and bright. When i put it back on i get no power.. Is that the video card? I tried both video cards from both monitors and they both did the same thing...also tried both screens. Any suggestions? Thank you very much.