Ubuntu – Ubuntu 15.10 boot hangs when starting Lightdm

I failed to read the release notes before upgrading to 15.10, I still had fglrx drivers installed. When rebooting after the upgrade it would hang indefinitely in the splash screen, I couldn't open a console with 'ctrl alt f1-6'. I was able to solve this by booting into recovery mode, opening up a root console purging the fglrx driver and installing the open source radeon driver. Now it hangs in this screen http://i.imgur.com/qAzaUtu.jpg

                               **System info**

• memory 15GiB System memory processor AMD FX(tm)-8350 Eight-Core
• Processor bridge RD890 PCI to PCI bridge (external gfx0 port B)
• bridge RD890 PCI to PCI bridge (PCI express gpp port B) display
• Tahiti XT Radeon HD 7970/8970 OEM / R9 280X] multimedia Tahiti XT

• HDMI Audio Radeon HD 7970 Series

                            **lightdm.log**
  

  [+0.00s] DEBUG: Logging to /var/log/lightdm/lightdm.log
  [+0.00s] DEBUG: Starting Light Display Manager 1.16.4, UID=0 PID=6021
  [+0.00s] DEBUG: Loading configuration dirs from /usr/share/lightdm/lightdm.conf.d
  [+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-greeter-wrapper.conf
  [+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-guest-wrapper.conf
  [+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf
  [+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-unity-greeter.conf
  [+0.00s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-xserver-command.conf
  [+0.00s] DEBUG: Loading configuration dirs from /usr/local/share/lightdm/lightdm.conf.d
  [+0.00s] DEBUG: Loading configuration dirs from /etc/xdg/lightdm/lightdm.conf.d
  [+0.00s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf
  [+0.00s] DEBUG: Using D-Bus name org.freedesktop.DisplayManager
  [+0.00s] DEBUG: Registered seat module xlocal
  [+0.00s] DEBUG: Registered seat module xremote
  [+0.00s] DEBUG: Registered seat module unity
  [+0.00s] DEBUG: Monitoring logind for seats
  [+0.00s] DEBUG: New seat added from logind: seat0
  [+0.00s] DEBUG: Seat seat0: Loading properties from config section Seat:*
  [+0.00s] DEBUG: Seat seat0: Starting
  [+0.00s] DEBUG: Seat seat0: Creating greeter session
  [+0.00s] DEBUG: Seat seat0: Creating display server of type x
  [+0.00s] DEBUG: Using VT 7
  [+0.00s] DEBUG: Seat seat0: Starting local X display on VT 7
  [+0.00s] DEBUG: DisplayServer x-0: Logging to /var/log/lightdm/x-0.log
  [+0.00s] DEBUG: DisplayServer x-0: Writing X server authority to /var/run/lightdm/root/:0
  [+0.00s] DEBUG: DisplayServer x-0: Launching X Server
  [+0.01s] DEBUG: Launching process 6033: /usr/bin/X -core :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
  [+0.01s] DEBUG: DisplayServer x-0: Waiting for ready signal from X server :0
  [+0.01s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
  [+0.01s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0
  [+0.01s] DEBUG: Loading users from org.freedesktop.Accounts
  [+0.01s] DEBUG: User /org/freedesktop/Accounts/User1001 added
  [+0.01s] DEBUG: User /org/freedesktop/Accounts/User1000 added
  [+0.28s] DEBUG: Got signal 10 from process 6033
  [+0.28s] DEBUG: DisplayServer x-0: Got signal from X server :0
  [+0.28s] DEBUG: DisplayServer x-0: Connecting to XServer :0
  [+0.28s] DEBUG: Seat seat0: Display server ready, starting session authentication
  [+0.28s] DEBUG: Session pid=6149: Started with service 'lightdm-greeter', username 'lightdm'
  [+0.29s] DEBUG: Session pid=6149: Authentication complete with return value 0: Success
  [+0.29s] DEBUG: Seat seat0: Session authenticated, running command
  [+0.29s] DEBUG: Session pid=6149: Running command /usr/lib/lightdm/lightdm-greeter-session /usr/sbin/unity-greeter
  [+0.29s] DEBUG: Creating shared data directory /var/lib/lightdm-data/lightdm
  [+0.29s] DEBUG: Session pid=6149: Logging to /var/log/lightdm/x-0-greeter.log
  [+0.31s] DEBUG: Activating VT 7
  [+0.31s] DEBUG: Activating login1 session c15
  [+0.31s] DEBUG: Seat seat0 changes active session to c15
  [+0.31s] DEBUG: Session c15 is already active
  [+0.31s] DEBUG: Session pid=6149: Greeter closed communication channel
  [+0.31s] DEBUG: Session pid=6149: Exited with return value 1
  [+0.31s] DEBUG: Seat seat0: Session stopped
  [+0.31s] DEBUG: Seat seat0: Stopping; failed to start a greeter
  [+0.31s] DEBUG: Seat seat0: Stopping
  [+0.31s] DEBUG: Seat seat0: Stopping display server
  [+0.31s] DEBUG: Sending signal 15 to process 6033
  [+0.76s] DEBUG: Process 6033 exited with return value 0
  [+0.76s] DEBUG: DisplayServer x-0: X server stopped
  [+0.76s] DEBUG: Releasing VT 7
  [+0.76s] DEBUG: DisplayServer x-0: Removing X server authority /var/run/lightdm/root/:0
  [+0.76s] DEBUG: Seat seat0: Display server stopped
  [+0.76s] DEBUG: Seat seat0: Stopped
  [+0.76s] DEBUG: Required seat has stopped
  [+0.76s] DEBUG: Stopping display manager
  [+0.76s] DEBUG: Display manager stopped
  [+0.76s] DEBUG: Stopping daemon
  [+0.76s] DEBUG: Exiting with return value 1

                           x-0-greeter.log

error writing X authority: Failed to open X authority
/var/lib/lightdm/.Xauthority: No such file or directory