I HAVE ANOTHER PROBLOM I DIDN'T MENTION .

I HAVE DELL OPTIPLEX 960.
I HAVE 6 GB OF RAM BUT WINDOWS SHOWS 5.87 GB USABLE I TRIED EVERY THINGS ON INTERNET LIKE ''MS CONFIG'' METHOD. NO MEMORY RMAPING IN BIOS .
TRIED EVERY THING,ALSO CHANGE RAM STICKS. I PUT MY RAM STICKS IN AN OTHER SYSTEM THAT SYSTEM SHOWS FULL RAM BUT OPTIPLEX 960 ONLY (5.87 GB USEABLE)
I FACE SAME PROBLOM IN MY OPTIPLEX 760 .

SYSTEM:
OPTIPLEX 960 (Q45 CHIPSET)

WINDOWS 7 ULTIMATE (64BIT)
6 GB RAM DDR2 (2X2GB 2X1GB) SAME .
INTEL CORE 2 DUO E8500 3.1 GHZ
NVIDIA GT 440 I GB DDR3 EVGA.

PLZ HELP ME.