If you hit ESC does it clear the freeze up? If that is the case it sounds like it is loading off-screen.
Press ALT + SPACE then M, then use the arrow keys to move the window around until you can see it.
Check out my Civil 3d blog at: http://c3dk.com/
Favorite Posts: Use Dynamo For Surface Analysis: https://youtu.be/eJNdX6guMP8
Fast Track your site grading with the new Corridor Workflow: https://youtu.be/Gg7u9-LgIL0