Hey OP, I had a similar problem installing my Girlfriend's PC and it drove me fucking insane.
Try breadboarding (assembling all the components out of case, on a non conductive surface ((like a wooden table or even the box your motherboard came in))) and see if that turns everything on. If it does, then your case is causing a shortage...for me it was a set of dodgy brass stand offs that constantly shorted the RAM and Mobo.
It's a shame you've found yourself in this situation. Usually building a PC is fine...but when you get to situations like this, it's heartbreaking.