I've been thinking about this.
When you heard the Loud Pop where was the motherboard sitting? On an insulated surface or on a conductive surface?
The two things that come to mind when you say loud pop are a capacitor blowing or a capacitor discharging through a conductive surface.
Trouble shooting: Remove the motherboard and place on a non conductive surface. With only the memory and CPU and a known good power supply what happens? You do not need a power switch to turn it on. You just need to momentarily close the two power switch contacts. Labeled PWRSW. Try with no Video card first, You just want to see if the fans run and if you can connect a speaker to the 4 pin speaker connector if there are any beeps as a first step.
Any chance you are still under warranty on the Motherboard?
From the English manual on this page
Don't forget you will need the 24pin and the 8 pin power leads from the power supply connected. The 8 pin supplies power for the CPU and The 24pin powers everything else.