I just bought a used cpu and motherboard seperate. They are a b360 and a i5 8400. When i first plugged them in i got a black screen. After a little troubleshooting i found that the left memory slotl is not working. The motherboard i have only have 2 memory slots. My ram still lights up when connected to that memory slot. I tried reseting the bios, but no luck there. Is it a dead memory controller in my cpu or dead memory slot on my motherboard?