One of the simple things to remember is most modern-day MB’s are dual channels. I am not trying second guess your ability or previous experience, it's the little things that can stump us at times. Usually slot 1 and 3, and or 2 and 4 are together. The order depends on the orientation from the CPU. Running only 1 stick of ram is not recommended as the controller is basically tripping over itself looking for the other ram channel. As another person noted I believe the speed of the ram is close to the limit for the MB. I have had similar issues and have had to change speeds slower not over clocking the ram or letting it run at its native speed. Hope this helps.