via the additional drivers menu I installed an new driver. (Can't remember which one) If ubuntu starts up I first see the ubuntu screen, but then it switches over to command line and asks for login.
I removed the video card from my PC and restarted with the monitor plugged in to the on-board video card. How do I restore the system to the situation I had before I made the change.
I tried to do it via the nvidia program, but as there is no card plugged in it does not function properly.