From the looks of your post, it seems that the motherboard has one or two damaged memory slots. Have you tried all four modules in the two slots that you know work? If so, do they all work? If so, then run a Memtest with each individual module in a working slot on the motherboard. If any of the modules give errors then the erroneous module(s) need to be replaced. You should be able to RMA them or at least use the warranty.