If, someday, your Intel-equipped computer should stop having OpenGL working in the X session, it may be due to the (completely useless) installation of NVidia/ATI drivers… so, open a shell and type in as follows:
sudo apt-get purge nvidia*
sudo apt-get purge fglrx*
sudo apt-get install –reinstall xserver-xorg-video-intel libgl1-mesa-glx libgl1-mesa-dri xserver-xorg-core
sudo dpkg-reconfigure xserver-xorg
sudo update-alternatives –remove gl_conf /usr/lib/nvidia-current/ld.so.conf
Syvo3 
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