Lately I was wondering why the heck my computer shows that I only have 3.95 usable memory, I searched some forums and youtube but still can’t find the answer. I entered my bios and it seems it has detected my 24GB memory. When I take a look at my motherboard I realized that the slots have blue and black color, I have 1 pair of 8GB memory and 1 pair of 4GB memory and I reseated my 8GB to the blue slots while 4GB on the black slot and powered up my computer. Problem fixed! Now my windows can detect all 24GB memory!
There might be some other causes but you can find other solutions on google if this one doesn’t work for you. Ciao!