Kind of rare case I would say. I have on my pc 2 sticks of crucial and 2 sticks of g.skill. all of them are 1600mhz ddr3 cl11 ect. they have been working together for months! today morning my pc won't post. I reinstalled them in different orders with no success... any combination within the first 2 slots works fine. the moment I try to add the 3rd/4th stick in, I get this continuous beeping postcode which is ram related. I have no idea what went wrong. desperate for your help guys!