It sounds as if the x server is not starting and you are being left at the command prompt. If the system is expecting a command line (terminal) login, log in. Then enter startx and see what happens: if it is obvious the system demands admin privileges, enter sudo startx.
I have no experience of Lightdm but if it behaves like gdm then it would run startx as part of its routine, so it might be instructive to try entering lightdm rather than startx before trying to start x manually as above. You shouldn't break your system trying out those two commands.
If I can find the notes I made when last I installed a GUI on a server -I installed gdm, though- then I'll get back to you.
In the meantime, good luck!