Unity is not working after upgrade to Ubuntu 15.10

Today I upgraded to Ubuntu 15.10, no errors happened during the upgrade but after the upgrade I can log in using my username and password but unity does not work. No launcher, no panel absolutely nothing just the background.

I tried to start unity myself using compiz --replace unity it gives me an error about a missing function definition in libunity.so and it fails to load.

Please can you help me with this?

[UPDATE]

output of sudo apt-cache policy libunity9 is

libunity9:
  Installed: 7.1.4+15.10.20151002-0ubuntu1
  Candidate: 7.1.4+15.10.20151002-0ubuntu1
  Version table:
 *** 7.1.4+15.10.20151002-0ubuntu1 0
        500 http://sy.archive.ubuntu.com/ubuntu/ wily/main amd64 Packages
        100 /var/lib/dpkg/status

[UPDATE]

After trying to follow the two answers the error message has changed as follows

DISPLAY=:0 compiz --replace unity outputs to standard error

  compiz (core) - Info: Loading plugin: core
  compiz (core) - Info: Starting plugin: core
  Invalid MIT-MAGIC-COOKIE-1 keycompiz (core) - Fatal: Couldn't open display :0
  compiz (core) - Info: Stopping plugin: core
  compiz (core) - Info: Unloading plugin: core

Reinstalling didn't work for me, as the problem was due to specific user files (~/.)

To get back your Unity launcher after an upgrade to Ubuntu 15.10, you can just open a virtual terminal Ctrl+Alt+F1, log in and then:

sudo service lightdm stop
cd ~
rm  -rf .gconf .gconfd .compiz .config/compiz .config/dconf
sudo service lightdm restart

That's all, it worked for me! My old installation had probably messed up user files, so removing them did the trick.

You might have an answer already, try a fresh install of Unity.

sudo apt-get update

sudo apt-get remove unity unity-2d unity-2d-panel unity-2d-spread unity-asset-pool unity-services unity-lens-files unity-lens-music unity-lens-applications gir1.2-unity-5.0 unity-common indicator-sound indicator-power indicator-appmenu libindicator7 indicator-application indicator-datetime indicator-messages libnux-2.0-0 nux-tools libunity-misc4 unity-2d-common

sudo apt-get autoremove

sudo apt-get autoclean

sudo apt-get install unity unity-2d unity-2d-panel unity-2d-spread unity-asset-pool unity-services unity-lens-files unity-lens-music unity-lens-applications gir1.2-unity-5.0 unity-common indicator-sound indicator-power indicator-appmenu libindicator7 indicator-application indicator-datetime indicator-messages libnux-2.0-0 nux-tools libunity-misc4 unity-2d-common

sudo apt-get upgrade

This should restore Unity.

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