Re:Booting failure

I was working on my PC and all of a sudden the Sreen went blank so I tried using another monitor but no avail.I have change the VGA and the Memory still no responding. Please what will be the possible cause even I don’t hear any beep or alert signal. Someone suggested that it might be from either Power supply or the motherboard. I don’t know because the Power supply is working properly and has no fault.so if it is the mother board how should I go about it to locate the fault?