My sons PC wont work?

Ok so, My sons computer was fine last night. today he tried to turn it on and the monitor wont display anything. tried 2 other monitors so i know its not that. i tried switching the ram around, trying one at a time, trying none at all. still nothing. the pc turns on fine, CD tray, all the lights, the fans, and HDD... show more Ok so, My sons computer was fine last night. today he tried to turn it on and the monitor wont display anything. tried 2 other monitors so i know its not that.
i tried switching the ram around, trying one at a time, trying none at all. still nothing. the pc turns on fine, CD tray, all the lights, the fans, and HDD all seem to work, only after pushing power about 15-30 seconds later all the lights shut off (unless there isnt ram in) but the pc is still on. So if it isnt the monitor, or ram, then whats up? he fry his mobo?
Update: I noticed that if there are NO ram sticks seated then the lights on the tower stay on, if any of the ram are in the lights go out. but i tested the ram in my pc and they work fine.
Update 2: I did try the on-board video and still nothing, so i dont think its the graphics card
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