Do you think a rig which doesn't have onboard graphic wud start without a discrete graphic card... Just asking this coz i have never tried booting my system without a graphic card...
Check and see if anythings shorting out the motherboard. Look for extra screws installed on the back, dust, etc.
Better yet, take the motherboard out of the cabinet, place it on a piece of cardboard and see if the problem persists.
