ASUS N55SF-SX384...with 8 GB RAM

i have 2 problems, please help...:

first: I buy 4GB of RAM and now I have 8 GB but windows show me in properities of computer 8GB (6.66 usable)...why? how i change it?

second: when I playing Call od Duty 4 Modern Warfare, 4 year old game, after cca 10 minutes of play the game freezes and restart system...windows 7....when is problem please? help me...

This post has been edited by Misco13: Dec 30 2011, 12:15 AM

Yes, I did it first. COD4 patch 1.7 and new driver for Nvidia. This problem do not only COD4. Assassins Creed 1 and 2 work perfectly. More games I didnt tried. Thanks

And problem with RAM ? You dont know?