I've just bought 4x matching 8gb ddr3 1600mhz ram to upgrade from my mixed 4x 4gb. They all work individually in every slot with no issue. They work in pairs in every slot (other than if I plug them into A1 and A2) but if I plug them into all 4 slots then I get a black screen. I've updated the bios and still no luck. Any suggestions as to why this is happening?