https://askubuntu.com/questions/124017/how-do-i-restore-the-default-repositories

you can use this trick. Open a terminal ( Pressing Ctrl+Alt+T ) and do these

Remove the corrupted one
sudo rm /etc/apt/sources.list
Open software-properties-gtk

sudo -i software-properties-gtk
This will open software-properties-gtk with no repository selected.

Then change the server to US or to any other server of your choice. You must enable some repositories from the new window in order to create new sources.list file in /etc/apt/.