i have found out the cause of the problem, thanks to you all...
the cause of the problem is that the fps rate is very slow at 60 fps
when i run the command """glxgears""" i came to know about that.....
i also went through elija's hyperlink and it is particularly because of him
now the problem i face is that there is no xorg.config file in debian 7
and how can i increase my fps rate
thank you