My computer keeps freezing?

Ok so my computer keeps on freezing when i am running games, i have to push CTRL+ALT+DEL then cancel to fix it. I went to best buy and asked why and they said ram. I have 4GBs and when im running my game (dragon nest) and i have FB open and music i only have 70% ram used, and even if I close them it stills freezes sometimes with 50% ram used. How can i fix this? plz help!
 
Two generic things to check until someone else comes to help is 1 make sure you aren't overheating your CPU. 2, update your video card drivers.
 
those both won't work its not my video card (its good i can run at high graphics) and ITS NOT MY COMP its the game and other games do it too.
 
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