[gmx-users] error in nvidia cuda installation

[Neda Rafiee]

Dear Stephane,
I followed the instructions in this link: http://www.steletch.org/spip.php?article89
With ctrl+alt+f1 I went to console, then I logged in and typed: sudo service lightdm stop
there was an error : Unit lightdm.service not loaded
Then I typed: sudo rmmmod nvidia 
I got another error : Module nvidia not currently loaded 
After that I typed: sudo apt-get --purge remove cuda* nvidia*
and using "sudo apt autoremove" I removed the suggested files. 
still in console, I typed : sh cuda_8.0.61_375.26_linux.run --toolkitpath=/opt/apps/pkg/cuda/8.0.61
-> Accept default location
-> accept the DRIVER ...And suddenly the page was changed to a very long description that at the end asked me to accept/decline or quit the session. When I chose "decline" or "quit", it would come out of the script, but when I chose "accept", it continued to ask me lots of questions about the location to be installed, OpenGL option, using -Xconfig or not, and many others with yes/no options. When I answered to all of the questions, a sentence appeared : "Installing the NVIDIA display driver..."
And after a while, it said:  "It appears that an x server is running. Please exit X before installation. If you are sure that X is not running, but still are getting this error, please delete any X lock file in /tmp. "
And then: "Driver installation failed !"

Would you please help me detecting the problem of CUDA with my system? I don't know if the problem is related to the Internet or another thing. What does the error mean by "X server" ?
Neda