MSI x399 MEG Creation RAM issue

[tep1981]

Corsair Vengeance LPX 4x 16gb 2666mhz, installed in the recommended slots but only 49gb is recognised, Windows reports the same that only 3 slots are in use, I've tried enabling A-XMP/reseating the memory in serial number order

I've used the same memory in my other Zenith Extreme board with no issues, albeit that was running a 2950x

Any other suggestions?

 

[tep1981]

I've tried each stick on the far right slot and 1 stick causes a no video signal, however when I use a the other 3 sticks and the suspect stick in another slot it does boot but as mentioned the motherboard is giving conflicting results
https://imgur.com/x3keaaJ

 

[tep1981]

No the single DIMM does not work in any slot, also if try and use the 4 DIMMS in a different slot configuration I get warning saying that these slots are not optimised or something like that