Here is the result of  "grep EE /var/log/Xorg.0.log" :

 (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[   350.468] (EE) Failed to load module "nv" (module does not exist, 0)
[   350.472] (EE) Failed to load module "vesa" (module does not exist, 0)
[   350.501] (EE) [drm] Failed to open DRM device for (null): -22
[   350.502] (EE) [drm] Failed to open DRM device for pci:0000:02:00.0: -22
[   350.503] (EE) Unable to find a valid framebuffer device
[   350.504] (EE) Screen 0 deleted because of no matching config section.
[   350.520] (II) Initializing extension MIT-SCREEN-SAVER
[   350.525] (EE) Failed to initialize GLX extension 
(Compatible NVIDIA X driver not found)

Shame on me, many errors.
I want to install the nvidia driver non-free,
this one is installed, downloaded on nvidia site : 
"NVIDIA-Linux-x86-340.107.run"

Thanks, regards.

André