How to change from Unity 2D to 3D?

I have been trying to run MyUnity, and it's been working fine until today, when it comes up with the message:

So, apparently I am running Unity-2D. So I did a little command-line search withecho $DESKTOP_SESSION and sure enough, it spat out simply "ubuntu-2d".

I have been using Ubuntu Tweak and perhaps I did something stupid in there, but I don't think it even had a feature like that. I've also noticed the clear differences in Ubuntu 2D to Ubuntu 3D, as well.

I have 12.04 Ubuntu. So is it possible for me to "revert" back to Ubuntu/Unity 3D?

Edit: My graphic card is a 2GB dedicated AMD Radeon HD 7750, which I've come to think needs to be upgraded 12.6 version. I'll try this and let you know the of the outcome, thanks so much for helping.

Result: after successfully updating the graphics card, I now can run 3D. Thanks so much to all of you and I'm sorry for such an unusual question!

Solution 1:

You can determine if you are running Unity 3D or 2D by open the system monitor. If you see a process named compiz in the processes tab, you are using Unity 3D. If it's running metacity instead, you're working with Unity 2D.

Ideas to get Unity 3D working:

1. First, install the package nux-tools and run /usr/lib/nux/unity_support_test -p in a terminal window. It will show if your hardware is supported by Unity 3D. If you have an Nvidia or AMD/ATI graphics card, you might have to install the proprietary drivers first to get (good) 3D support. If it says Unity 3D supported: yes, you can continue with the other steps. If not, you cannot use Unity 3D.
2. Install Unity if it's not installed by running sudo apt-get install unity gnome-session.
3. Now log out, there should be an Ubuntu logo next to your username in the login manager. Click on it and select "Ubuntu", and log in again. Unity 3D should start.
4. If it's still starting Unity 2D and not 3D, open a terminal and type unity --replace. Unity 3D should start, if not, the terminal output might be interesting.
5. If all above doesn't work, create a new user and log in. Don't forget to select "Ubuntu" as in 3. Maybe some of your old user's preferences are broken, a new user will start with fresh preferences.

Solution 2:

I suggest you to have a look at the 2 answers of that question
You will learn out to configure the file /etc/lightdm/lightdm.conf