I've had this problem before where the dual monitor setup would not be kept (i.e. I had my right screen as the main screen, but after restarting, the position of my right screen would be shifted to the left.), did a fresh reinstall and the problem got fixed (probably some other DE configs overriding each other since I had KDE, Gnome and Unity).
However, the problem now is that the dual monitor setup would be still broken on the login screen (my right screen would become the left one) and the screen config would only be fixed after I had logged in.
Best Answer
Install
arandr
by pasting the following in terminal:Open arandr. Your screens are probably configured how you like. If so, go to Layout > Save As. Open the saved script and copy the entire
xrandr
command.Create the file /etc/lightdm/lightdm.conf if it is not created already. You can use:
Now paste the following. Replace my
xrandr
command below with your own.Reboot and your login screens should be correct.