How to freeze screen to enable menu interaction?

I'm creating a simulation and would like the end user to be able to click on the screen, have the screen freeze and then be able to click on a simple navigation menu that's in the upper right corner of the screen. Currently, the viewpoint (it's first person) moves with the cursor all the way until they make a selection.

Any help would be greatly appreciated. I'm using Java, but C# would be fine as well.

Thanks!