I seem to have a similar problem. I'm trying to install Nvidia drivers with no luck so far. There is another thread here with a solution to install gdm as default while keeping mdm and/or lightdm etc. driver install went smoothly for that poster. I thought I would try the same but came up with the trying to overwrite .......nobody.png and broken pipe . That is being brief. I will gladly paste all the contents of a text file I have been updating on this subject if that would be helpful.
Basically I want to install gdm while leaving mdm intact and proceed with driver install. possible?
i5 3570k, ASRock z77 Extreme 4, 8 Gb Ripjaws 1600, Antec 430w psu, HVR 1600 tv tuner, custom case- marble top, oak face. Carver & DCM Time Window sound system. Mint 14 KDE.