I recently purchased a Mac Pro for my roommate and in the last couple of days whenever he wakes the computer from sleep, there's a "black box" that looks like some kind of text field left over from something that appears on the display. We can't figure out how it got there, or how to remove it. When you try to click on it, the mouse pointer just moves behind it. This only happens when the computer wakes from sleep. When restarting, it's gone. Any ideas? :O)