ok, the problem is solved now, i dont have any other problems except one; when running a full screen game the computer automatically turns off and a blue screen comes. it says :
An error has occured and windows has shut down blablabla
Attempt made to write read-only memory.
Make sure new hardware or software is properly installed
That would just make the computer not restart anymore, it won't solve the cause of the problem. I did that too, it is good because It gives you a chance to fix the problem without worrying that it would restart.