Comment 5 for bug 854431

I found out that lightdm-gtk-greeter works, after I had a second look into lightdm.conf. (comment #2)

It is actually unity-greeter (0.1.1-0ubuntu1) that fails. Instead of showing the greeter, there is blank screen and hard disk indicator led blinks actively. The keyboard is unresponsive for a while: you cannot enter tty1, caps lock indicator led is not turned on, but then after about 10 seconds from pressing the keyboard the HD led is turned off and the keyboard starts to work normally. Probably this is a subject of another bug report.

The greeter can be changed in /etc/lightdm/lightdm.conf. I simply commented the unity-greeter. Reinstalling nvidia-173 or nvidia-common did not help.