That's alright, all you do is hold a screwdriver to the two power pins on your motherboard for just a second, it does the same thing as if you were pressing the power button.
Hmm :/ I assume you double checked your power connections, if not do that. That's about all I got, sorry But someone more knowledgeable may be able to help you out further.
I know this probably is the last thing you want to hear but you could also try contacting Asus and see if you can get it replaced. There is a 2% chance that you happened upon a defective product.
Also, regardless of how much or how little you may know about building a computer, I'd recommend watching the 3 part series of how to build a computer that I linked above (at least the 2nd part), it contains just about everything you need to know about building a computer.
Still need hardware details. Take the board out of the case and place it on your motherboard box. Take all cards off and leave only one ram stick plugged in. Leave drives unplugged. Try to turn on your PC then. If it turns on and stays on then plug everything back in one piece at a time. If it all works it's your case. Make sure the stand offs and screwed in properly.