You will need to go under the "Start Menu" to the "Programs Folder" and look in the path: Unigraphics V18.0\Unigraphics Tools\UG FLEXlm for "UG License Options" which will open the following screen.

Highlight UGACAD under the "Available Bundles" column above and click the "ADD" button. Now you should have a screen that appears like the one below and you can click the "OK" button and you can now use Unigraphics.

Now you can use Unigraphics.