I remember having an issue like this years ago, but I no longer use a dual monitor setup so I couldn't remember how to fix it. But basically when playing fullscreen games on one of his two monitors, when he clicks to shoot or whatever, sometimes the game will lose focus or act like he alt-tabbed out. He has to unplug his second monitor to get around this. I wasn't sure how to help him. I wasn't sure whether to put this in General Hardware or Software because it could be a software/driver issue, or a monitor issue...