Did you try every stick independently? In other words, did you try each stick by itself in 1 slot? Also are all 4 sticks identical in speed/capacity/manufacturer? If you did not try all 4 by themselves, you may have 1 bad stick. However, last time I had Windows diagnostics tell me I had bad memory (one or two of 4 identical sticks actually "failed" the diagnotic test), it was actually due to a RAM failure on my graphics card. I replaced the card, and all was solved. Hope this helps