Switch from NVidia to internal Intel HD graphics - OpenGL does not work
You need to remove the nvidia drivers so that the driver does not try to get itself loaded instead of your Intel card.
Normally no further installation of drivers is required for the Intel built in driver but if the nVidia driver is getting loaded it will take over.
sudo apt-get purge nvidia*
Remove your xorg.conf
sudo rm /etc/X11/xorg.conf
Reinstall xorg completely
sudo apt-get install --reinstall xserver-xorg-core libgl1-mesa-glx:i386 libgl1-mesa-dri:i386 libgl1-mesa-glx:amd64 libgl1-mesa-dri:amd64
Re-configure Xorg
sudo dpkg-reconfigure xserver-xorg
Reboot
sudo reboot