We have a bug logged that seems to be related to having Webroot installed on the machine.
[BUG-000086476: The Zoom In, Zoom Out, and Pan tools from the toolbar become stuck in ArcMap after pressing the corresponding Z, X, and C hot keys.] I didn't want to just jump to that conclusion on this post before I heard back from one of you.
We're actively investigating this issue, but unfortunately, for now there is no listed workaround. I'm not familiar with Webroot, but is there a way to quickly disable it. At least for testing, you might disable it, work in Pro and see if it alleviates the behavior.