Bolas, long shot, but................all connections are good? 12v ATX top left is OK?
Graphics connectors OK? Is the Graphics seated OK? Main mbd conn seated? Is your PSU capable? You get no display, do you have heavy load on the graphics side, xfire?, SLI?
I don't mean to patronise, but, maybe the mbd is not getting past the initial loading sequence before it even gets to POST
Another issue could be that when you installed the CPU the mbd skt might have sustained a bent pin.

Just a couple of suggestions