When you press OK in this screen you probably get to a console prompt. At this prompt, run the following commands:
*Notice the X in /usr/bin/X is uppercase ok?
sudo service lightdm stop
sudo kill -s $(pidof lightdm)
sudo service gdm stop
sudo kill -s $(pidof gdm)
sudo killall -s KILL /usr/bin/X
... again and see if the installation proceeds beyond this screen.
** Press OK for all the questions of the NVIDIA install. Let me know when the install finishes. We need to do a few more couple things.