In my Ubuntu 12.04.2 with GNOME-Shell I'm not able anymore to run any graphical programs with
I always get an error like
cannot open display
I noticed also that I'm not able anymore to install extensions from the website, but I think it's not related, of course I'm not sure too :)
I've already spent time and effort searching the topic everywhere and the few I found didn't give any solution for me. I don't want to reinstall.