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BIOS says 16gb of ram, windows says 12gb

bios and cpu-z both say 16gb of ram installed windows and task manager both say 12gb installed and control panel has only 60mb reserved and also ram slot 3 and 4 dont work i have to go to asus bios and disable DRAMM b slot 1 and put the stick to slot 1 for some reason, if i have all ram spots enabled then the pc wont boot with 3rd ram stick in 3rd of 4th spot. I have 4×2 4gb sticks and 1 8gb stick all hyperx fury sticks, my motherboard is asus pro b250