It sounds motherboard to me before you bought the new parts, and having the same issue makes it further sound like it. Since it's usually capacitors that go on motherboards, whos job is to hold voltage in quantity and discharge it in a single go the voltages around the motherboard can get weird before it just dies. Just a thought.
I guess that sounds to be more like it, then. The motherboard was purchased in 2009, so this leaves me more towards that idea. Plus the fact that I would have a dead power supply and video card (both brand new) would be unlikely.