Well it could be a few things.
Take everything out except the CPU, Ram and video card and listen to the posts beeps you get. Those are the error codes. There will be a corresponding entry in your mobo manual for each.
I would imagine if you get no beep that it is the CPU, or the motherboard.
Good call letting your friend try your CPU in his computer, as it may be the motherboard. If it is the motherboard you could try to RMA it as long as you didnt damage it.
Also, repost that information from your original post, it is critical to helping you out, and a clickthrough can be a bit of a pain