1| Can you please pass on your full system's specs inclusive of your OS, connected peripherals and any after market cooling? Since this is dealing with a before and after scenario, it'd help us if you could list your parts as a before and after listing.
2| Have you tried transplanting it back to it's original chassis? If the system works on the older chassis after replanting then the new chassis has a grounding issue. Please make sure your motherboard stand offs are all in order while noting if the motherboard is not touching any part of the chassis.
3| You're sure that no LED's on your board are lit up to indicate no power is being delivered to your board?
The thread's title area should hold the issue in a clear and concise manner...