Is my ram dead or is it the socket?

[mineclub8]

I builded a pc with my friend and everything was fine. But after a few times used my taskmaneger said that is had only 4 gb of ram but i had 2 sticks of 4 gb my bios says that i have 2 dimm slots used and it shows me 4 gb of ram what is the problem here pls help

SPECS:
mobo:B350 tomahawk arctic
cpu: ryzen 3 1200
gpu: gtx 1050 ti
ramm: ballistix sport 2x 4gb 2666mhz ddr4
psu: be quit system power 9 500w

 

[clutchc]

Try each stick alone in the suspect DIMM slot.
Try each stick in the good DIMM slot.