Hi I have look around at other threads and nothing has helped so I thought I should ask. I recently just installed 2x http://gskill.com/products.php?index=355 [F3-12800CL9D-8GBXL 2x4GB] when I go into BIOS it ownly shows 4gb as usable, I tried changing to D.O.C.P and X.M.P but both had no effect. Resource monitor shows 4gb useable 4gb reserved.
Try plugging your RAM modules into different slots. And even different combinations.
Try and plug in each module individually and see if the system can bootup and recognize the full 4gb from each stick.
I feel it has been said but seriously read the manual carefully. Sometimes they are very very specific for memory best practices. Perhaps the RAM brand is not recommended for the motherboard. Unlikely but still possible.