Black screen with startx

When I do "startx" I get a black screen "with a white square in top-left".

My graphics card is a "nvidia gtx 660 ti" and my xinitrc:

setxkbmap es
exec mate-session

Anyway I did try with twm or launch directly with "exec mate-session" and I get the same problem. Nvidia module is load in the kernel correctly and I did use "nvidia-xconfig" command to configure xorg.

My /var/log/Xorg.0.log is:
Thanks you.