Dell xpsl702x motherboard upgrade

Hello everyone, I have a problem and dont no how to resolve it.I have dell xps l702x.i3 2.10ghz,4gb ramm,nvidia gt550m 1gb,my mother board burned and I thought to replace it with the gt555m 3gb with 4 dimms  slots,I replaced it and I put in old memory..old CPU. i3...laptop switched on...but screen is black..there is no image...and fan its very loud....please help me.I don't now what to do..thanks very much