Recently upgraded to 15.10 and that looked okay at first. However, the displa driver that it installed, NVIDIA, was causing issues. So I defaulted back to the open source driver and reboot. MISTAKE! Ended up causing the system to crash and couldn't do anything about it.
I rebooted into root terminal. Then ran a command to display the available drivers.
The spit out a list of drivers. Then I reinstalled the latest available nvidia driver.
apt-get install nvidia-352-updates