In "Full Screen Photobooth Mode" press up/down on the keyboard to manually change exposure on the live view. When you go back into the main menu you will notice that the shutter speed is no longer set to 1/200 so please change it back.
If you do not own a T3i and are experiencing a dark live view before the picture is taken, then you need to change your movie mode to "Exposure Simulation"
Change it to "EXPOSURE SIMULATION" Not "STILLS DISPLAY"
