My PC is running a xeon x3430, with an asus p7h55/usb3 motherboard. Windows knows I have 8gbs installed. My memory is a 2x2gb kit of xms3 1600mhz, and 2 other xms3 modules that are part of a 3x2gb kit. The motherboard is rated to run 16gbs of memory in a 4x4gb config. Why is my memory not usable?