So i was going to upgrade my RAM for my computer I have a 4 ram slot and have 2 256's and 2 512's. I have a yr old computer and went out and bought 2 more 512's and ended up not having the ram fit. I was one slot off from making it fit into the slot. I bought 512 PC5300 DDR 400. It didn't fit. I am going to return it, but what RAM should I buy. The computer is all PCIe and it's just very frustrating.