|You provided decent info about everything but the power supply. Is it a decent name barnd unit - Antec, Corsair, ThermalTake, etc? Or a $15-20 cheapie?|
The 4-pin ATX12V plug MUST be connected to the motherboard, that is what sends power to the CPU. Without it, the fans & other hardware may work (or appear to work), but there's no way the system will boot without it.
You should have benchtested your hardware. Obviously if it didn't work on the becnh, you would have saved yourself the hassle of assembling everything inside the case.