My Ubuntu 15.10 install breaks graphics when installing new nvidia drivers for my GTX 970. After the update, the hardware acceleration doesn't work as evidenced by:
Cinnamon telling me (unity is also affected)
Steam not starting with this error "X Error of failed request: BadValue (integer parameter out of range for operation)"
Overall slow UI graphics
nvidia-settings is empty https://i.stack.imgur.com/fOVxS.png
I did the update via "Additional drivers" from the graphics-drivers ppa, from which the initial installation was done. Then, after it did not work, I tried a "sudo apt-get purge nvidia*" then I installed nvidia-364 from the command line, still not successful.
"lspci -vnn | grep -i VGA -A 12" says that the kernel driver is nouveau and any attempt to blacklist nouveau makes the Desktop environment not boot. Also this command list my Intel iGPU first, which is disabled in the bios and has nothing connected to it.