The solution to your "my desktop is blank in Unity (3D)" is simple, but involves using an advanced tool, Compiz Config Settings Manager.
Warning: Compiz Config Settings Manager is an advanced tool and one tiny mistake, typo or an accidental click of the mouse can leave your desktop unusable, requiring time and effort to fix it. Please be very careful and follow instructions...thanks. Once you are done using it, please consider uninstalling/removing it to reduce future risk. If you mess up, please see this answer on how to fix things.
- Install CompizConfig Settings Manager with
sudo apt-get install compizconfig-settings-manager in Ubuntu 2D, if you don't already have it.
- Logout and log in into Ubuntu (3D)
- Right click on the blank desktop, create a new folder.
Click on "File System" on the left sidebar, and navigate to
/usr/bin. Scroll down to CCSM and double-click to run it:
unity in the Filter box and click on the Unity Plugin:
Just check the "Enable..." box on the bottom left and you should have your normal 3D environment back: