The memory slot number refers to the physical positin, not th eorder that you load the memory .
Slot 1 is at the far right, and to the right of the processor are slots 1,2,3,4. To the left it continues 5,6,7,8, and all this is printed in tiny numbers on the motherboard.
So, take out that far right memory stick and carefully clean both sides of the contacts with 70-90% IPA (not the beer type). Or, use DNA for that. Then reseat. That will usually fix it.