windows 7 not using all 8gb of ram

System Manufacturer/Model Number: Custom (Self Build)
OS: Windows 7 Home Premium 64bit
CPU: Intel Core i7 2700k
Motherboard: eVGA P67 SLI
Memory: 8GB Mushkin Redline Ridgebacks @1866
Graphics Card: EVGA GTX570 SC
Sound Card: XiFi Titanium HD
Monitor(s) Displays: LG W2453V
Screen Resolution: 1920x1080
Keyboard: Saitek Cyborg
PSU: Seasonic x750
Case: Corsair 600T SE White
Cooling: eVGA Superclocked CPU Cooler
Hard Drives: Intel 320 80GB -- Intel X25-V 40GB --WD Black 1TB x2 -- WD Blue 640GB
Browser: IE
Antivirus: Kaspersky
Other Info: LG BD/DVD

OS: Windows 7 64-bit
CPU: AMD Phenom II X4 955 BE
Motherboard: MSI nForce 980a
Memory: G-Skill 1600MHz 8gb DDR3
Graphics Card: Geforce GTX 470- OC'd to 635 core clock
Sound Card: On board
Monitor(s) Displays: 24' Samsung LCD
Screen Resolution: 1920 x 1200
PSU: 850 Watts
Case: Xcilio Windtunnel
Cooling: Fan
Hard Drives: 1 WD 500Gb 7200rpm 1 WD 1Tb External
Internet Speed: 15 down 5 up

Computer Type: PC/Desktop
System Manufacturer/Model Number: Built them myself, Science Experiments !
OS: Win7 Enterprise, Win7 x86 (Ult 7600), Win7 x64 Ult 7600, TechNet RTM on AMD x64 (2.8Ghz)
CPU: AMD fx8350 4ghz, AMD-32 2400mhz, AMD-64 3200mhz, AMDx64 2.8G
Motherboard: SIS 755, ECS-K8M890M-M (Ult 7600), GigaByte & others
Memory: 2gb, 4gb on the Ult 7600, 4gb on Technet RTM, 32gb on FX8350
Graphics Card: Draw my own Graphics, several nVidia cards
Sound Card: on motherboard
Monitor(s) Displays: 19" flat scr, 28" I-Inc widescr,22" Emprex Widescr, 23" Acer
Screen Resolution: 1280 x 1024, 1440 x 900, 1920 x 1080
Keyboard: Compaq & Dell recycled from GoodWill
Mouse: Made in China Optical Wired Mouse
PSU: 430w, 550w, 600w, 700, 800, etc
Case: All Generic Full Towers
Cooling: Open Air & a few fans, some w/ colored LEDs
Hard Drives: 6 pata Ide HD's & 2 Sata HD's added 80gb external on Ult 7600 computer, numerous extra 1tb, 2TB, 3Tb SATA HD's A collection of ext HD Docks w/ HDs
Internet Speed: Fast Cable InterNet
Browser: IE 8 is preferred, but use FireFox sometimes
Antivirus: AVG Free on 24 different Desktops, NO Problems!
Other Info: Linksys Routers, switches, & Hubs Too Many USB Flash Drives to count, Biggest is 64GB ! Eight computers in my home network. Sixteen computers at my business network. Linked via TeamViewer ! Lots of old used spare computer parts everywhere!