One stick is from TEAM GROUP the other one is from G. SKILL. But they're both 2666freq. and DDR4. I have tried using just the undetected one and the monitor would say "CHECK CABLE CONNECTION"does these ram are same model and name did you try to use the non detected one in the first slot alone and do the same with the others could be a defective one .
4Gb- Team Group DDR4 4GB 2666MHz CL19 1.2Vexact model of the ram stick?