Best Solution

Remove .config,.local, .cache and .fontconfig from your home directory will make your system as it was a new

Follow these simple steps

• Open terminal(CTRL+ALT+T, if terminal does not then press CTRL+ALT+F1 to go to CLI tty1 mode) first make a directory as a backup

  
  
  

  cd ~
  
  
  
  mkdir backup
  
  




• Then copy above mentioned directories to backup

  
  
  

  cp -R .config .local .cache .fontconfig backup/
  
  




• Then remove all mentioned directories:

  
  
  

  rm -r .config .local .cache .fontconfig
  
  




• Then restart your system

  
  
  

  sudo reboot
  
  




• That's it.. Your system will be rebooted in new default configuration.

Try these if above mentioned steps didn't help

Method 1

You just need to turn the Unity plugin back on:

1. Press Ctrl+Alt+F1 and log in.



2. Install compizconfig-settings-manager:

   
   
   

   sudo apt-get install compizconfig-settings-manager
   
   




3. Then run it by doing this:

   
   
   

   export DISPLAY=:0
   
   ccsm
   
   

   
   
   

   The first part tells the terminal which display you want it to load on (otherwise it won't have a clue).




4. Press Ctrl+Alt+F7 (or Ctrl+Alt+F8 sometimes) to get back to the graphical display where there should be a CompizConfig Settings Manager screen sitting there.




5. Find the Unity plugin. Enable it.




6. Everything should spring into life but if it doesn't, you might have to restart. You can do that by going back to TTY1 and running sudo reboot.

Method 2

For 12.10 and below:

Press Ctrl+Alt+T for a terminal and run ccsm, then re-enable your 'Unity' plugin.

You also may then need to run a unity --reset.

In 13.04:

unity --replace is deprecated. Instead, use the following:

dconf reset -f /org/compiz/ 

unity --reset-icons &disown

Reboot if it doesn't work right away.

_{Source: Unity doesn't load, no Launcher, no Dash appears}