it seems to be the set up of my screen who is not correct
What do you mean by that? That there is something wrong with the settings for the monitor or something wrong with the settings for X?
The solution for settings for X is in the troubleshooter. If it is your monitor settings that's wrong you could edit xorg.conf following the troubleshooter, but post back if this is the case
Don't fix it if it ain't broken, don't break it if you can't fix it