I'm using 14.04 LTS with unity, but i removed the ubuntu desktop and installed the gnome ubuntu desktop instead, since unity has given me some errors... The thing is, im happy with gnome, but the login / lock screen is the one from ubuntu and not gnome. During the installation, i was questioned if I wanted gdm or light dm, I choose the light dm, is it the problem? was i supposed to choose gmd?
Run any one of the following commands -
sudo dpkg-reconfigure gdm or
sudo dpkg-reconfigure lightdm
Select the display manager you want to use by default and hit enter. Then, restart your computer.