W7 x64 won't see more than 3gb Ram

Computer Type: PC/Desktop
System Manufacturer/Model Number: Own build
OS: Windows 7x64 Home Premium SP1
CPU: Intel i7 2600k
Motherboard: ASUS P8Z68 Deluxe
Memory: G.Skill Ripjaws (DDR3-1600) 2x4GB
Graphics Card: Nvidia GeForce GTS 450; Intel HD Graphics 3000(GT2+)
Monitor(s) Displays: Dell Ultrasharp IPS panel U2311H, Samsung SyncMaster P2350
Screen Resolution: 1920x1080
Keyboard: Logitech MK520 (wireless)
Mouse: Logitech MK520
PSU: Seasonic M12II 520W
Case: Lian Li Lancool PC-K60
Cooling: Case: 1x120mm, 3x140mm CPU: Hyper 212+
Hard Drives: Samsung 850 Pro SSD 256GB, Samsung SSD 840 120GB, Seagates 1TB Barracuda ST31000528AS x2
Internet Speed: 6-7 Mbps
Browser: FireFox
Antivirus: Norton Security Premium, Malwarebytes on 2 (MSE on 3rd PC)
Other Info: Audio: Logitech Z523 2.1