It would help if you also posted your /etc/X11/XF86Config-4 file. There are modifications that must be made, ie:
1) Remove / comment out the lines "Load GLCore" and "Load dri" in the module section.
2) Add the line "Load glx" in the module section.
3) Change the driver to "nvidia."
These steps are covered in the documentation. If you still have difficulty, you can use my XF86Config-4 file (Underneath my signature) as an example.
"Floating in a dream-like state, I am the emporer of a parallel universe." --Arch Enemy
My xorg.conf file