I solved my issue 
:
- Esc on boot: grub menu
- Advanced options
- Enable networking
- apt-get update && sudo apt-get dist-upgrade
- apt-get clean && sudo apt-get autoremove
- apt-get remove nvidia-340
- Reboot
I hope it was a good and clean solution, but It works now and I'm back with the Xorg driver and I just made a system backup 
.
I wanted to install the Nvidia driver to enable h.264 hardware decoding support for video playback and have the VDPAU option in Kodi.
Is installing an Nvidia driver for my 8600 GS the solution for this, and if so, do you know why installation via additional drivers does not work?
Thanks