I'm using a laptop with external monitor (laptop screen disabled). I had a power failure in our house so laptop (without battery) closed, I had a lot of stuff opened and something broke because Ubuntu was not able to boot, so I went though recovery mode and it was ok except for one thing. Login screen will not appear on external monitor as it did before. The blue Xubuntu loading picture appears first, but then it freezes and login screen pops up only on laptop (with different background picture, which changes if I plug/unplug the VGA cable), after login, it works fine. Can you please help me?
Looks like your should simply go the Settings - Monitors and set your external display as primary. Or go to the NVIDIA X Settings, set you monitor and save your configuration to X configuration file from there (Xorg.conf). I think it should help.