Okay, so you found out it worked while breadboarding. Double check when you put the setup in your case that you have the standoffs right.
Did you install the standoffs under the motherboard? Did you place them so they all align with the screw holes in the motherboard, with no extra standoffs touching the board in the wrong place? A standoff installed in the wrong place can cause a short and prevent the system from booting.
Wait.. the case came with standoffs? What exactly are standoffs?
All we did was set the motherboard in the case, align it with the holes, and screw it in?