Click the wrench icon on VoiceAttack's main window, then on the "System / Advanced" tab of the VoiceAttack options window click "Reset Screens", check the "Close VoiceAttack now" box, and click "OK".
If that fixes the issue, you changed your display configuration at some point, causing a window to appear offscreen. Because VoiceAttack windows are modal, I.E. an existing window cannot be interacted with while a child window is open, that would give the appearance of a freeze.