If you want to display Computer,Home,Network,Trash and Mounted volumes icons on ubuntu 12.04 (Precise) desktop follow this tutorial
Preparing your system
Open the terminal and run the following command
gsettings set org.gnome.desktop.background show-desktop-icons true
Now you need to restart your ubuntu system before running the following commands.
Run all the commands from your terminal
For Computer Icon
To show the Computer icon run the following command
gsettings set org.gnome.nautilus.desktop computer-icon-visible true
To hide the Computer icon run the following command
gsettings set org.gnome.nautilus.desktop computer-icon-visible false
For Home icon
To show the Home icon run the following command
gsettings set org.gnome.nautilus.desktop home-icon-visible true
To hide the Home icon run the following command
gsettings set org.gnome.nautilus.desktop home-icon-visible false
For Network icon
To show the Network icon run the following command
gsettings set org.gnome.nautilus.desktop network-icon-visible true
To hide the Network icon run the following command
gsettings set org.gnome.nautilus.desktop network-icon-visible false
For Trash icon
To show the Trash icon run the following command
gsettings set org.gnome.nautilus.desktop trash-icon-visible true
To hide the Trash icon run the following command
gsettings set org.gnome.nautilus.desktop trash-icon-visible false
For Mounted Volumes
To show Mounted Volumes run the following command
gsettings set org.gnome.nautilus.desktop volumes-visible true
To hide Mounted Volumes run the following command
gsettings set org.gnome.nautilus.desktop volumes-visible false
After enabling icons should show similar to the following screen