Let's do it manually then.
Make sure you removed the one you installed from the site:
Replace "NVIDIA-Linux-xxx-xxx.xx.run" with the actual name of the script you downloaded.
sudo NVIDIA-Linux-xxx-xxx.xx.run --uninstall
Clean the house:
Then restart your machine.
sudo apt-get purge nvidia-*
sudo rm -rf /etc/X11/xorg.conf
Once you get into the desktop again, install the Steam driver:
Create the X config file:
sudo apt-get install nvidia-experimental-310
Restart. Now you should be using the proper Nvidia driver for Steam.
Let us know how it goes.