Oh man, now I feel really stupid!
I had only to explanations to change the xorg.conf :
- Do it manually with mousepad /etc/X11/xorg.conf
- xorgcfg -textmode
These two options never fonctioned for me.
Now I read your replie and saw xorgconfig
Just tried it and I was able to set everything perfect.
I just don't know what to say and I don't understand why nobody told me about this option before.
So thanks a lot for the help, your answer had just the information I needed
Sorry for all this though