I was downloading some updates like almost every day so a message about some files to remove or replace I think (I'm not sure) has appeared and I've accepted to replace without knowing -I confess- what is it about, I've had to restart PC to go to Windows 7 for something and have forgot that downloads and installations on Ubuntu were not finished.. The result: after a comeback to Ubuntu (12.04),the message: -failed to load session Ubuntu- has appeared and lower graphics in both two sessions -guest and mine- and after accepting my password, can't us my mouse, then I realize that between downloads were an update to ubuntu 14.04lts I refused before but decided that day to add to downloads and instal it.. so may be it was the cause of the issue after I have suddenly cut installations by restarting my computer to go to win7. I was searching in Ubuntu by Windows some answers and I've tried in terminal after starting PC:
sudo apt-get update sudo apt-get install ubuntu-desktop sudo apt-get install -f install sudo dpkg-reconfigure ubuntu-desktop sudo reboot
sudo apt-get update sudo apt-get install unity-2d sudo apt-get install ubuntu-desktop sudo apt-get install compizconfig-settings-manager sudo apt-get install compiz-plugins-extra sudo apt-get update
/ sudo apt-get install gnome-session sudo apt-get install lightdm sudo apt-get install unity-greeter sudo dpkg-reconfigure lightdm
sudo apt-get install ubuntu-session
and many others I forget but always fail in the end by:enable to fetch dz.archive.ubuntu.com I couldn't find something satisfying in launchpad about replacing my archive source and it was a little hard for me to understand.. I'm in 12.04 lt's since 2 years and months, that the first prob like that. Hope you help me.