Try swapping the slots. What I mean is, take out the 4gig RAM from whichever slot it is in, and put the 2gig RAM in that same slot. Now put your 4gig RAM in the slot that your 2gig RAM was originally in. I believe the trick to make this work has everything to do with the slot that it is in. I can't remember if it's the left slot or the right slot, but I think only one of them will recognize that 4gig RAM.