Can't get past LightDM with NVIDIA driver

[Matthias]

Every two or three weeks or so my laptop won't load unity anymore. After login from LightDM it just respawns to LightDM. The only work around i found is to purge the NVIDIA driver and reinstall it from the terminal. Gnome fallback doesn't work either, only the metacity or terminal from rescue mode.

sudo apt-get remove --purge nvidia-*
sudo apt-get install nvidia-340

I assume that the NVIDIA driver simply doesn't load under certain circumstances. Sometimes this gets triggered when the laptop runs completely out of battery, but it can also happen with a proper reboot.

lsb_release -rd
Description: Ubuntu 14.04.3 LTS
Release: 14.04

Expected behavior: Unity loads
Behavior: Respawn to LightDM