Just did a fresh install of Ubuntu 15.10 on a machine fitted with an NVIDIA GTX 970 video card and it didn’t work properly, clearly due to a video driver problem. In fact, the Displays option on Settings crashed! Seems that this version isn’t automatically installing the correct video driver for the card. This can be done manually after the install by using a terminal window to enter:
sudo ubuntu-drivers autoinstall
After a reboot, the system should come up correctly.