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#21
This configuration just indicates slot to be used, if running dual or 3 channel. Single stick run as single. At the bottom it's saying one stick goes into 1st slot.
Motherboard could be a problem. Load optimized defaults again, or even reflash the latest BIOS. Check CPU again (I know you did) - some of CPU's pins are controlling the memory.
Edit: take care, that slot 3 and 4 are populated with same memory sticks. You said you bought same type, but they are different. No chance you're gonna get the same chips after 4 or 5 years.
Think you've done everything there is to be done. Check about same sticks again (in slot DDR_3 and DDR_4).
One more thing to check: in Advanced Chipset Configuration check UMA Frame Buffer Size. If there is something like that.. This is memory for integrated graphic. Don't know if your CPU has it at all..