Make sure you video card is supported by SOE. Currently there are a few cards that will not show the 3D Ring because they are not supported by SOE. Roger Sewell was nice enough to post more information on this here. There is also more information if you search on this subject on how to use a 3rd party program to make your unsupported video card work with the 3D Targeting Ring.
If you found that your video card is supported and your still not seeing the 3D target ring make sure you have the following files in your custom interface folder:
You will also need to login to the game and in the options window enable the 3D Targeting Ring. You will then need to log out of EQ entirely and log back in before it will show up.