Dell 15R N5010 graphic shows "Standard VGA Graphic" and graphic stretched

I have a dell Inspiron 15R N5010 laptop.

windows 7 64-bit OS  Recently I have face some issue so i re-install the OS

Now it shows Standard VGA Graphics Adapter.

now my display is not upto the mark. In screen resolution i used to get a resolution of 1366 x 768 in MOBILE PC DISPLAY MODE.

so now the display is really wierd and stretched.

So please help me to find the actual drivers which are needed.

plz reply back. :)