hello. i have a macbook pro with a widescreen 19' monitor. sometimes when i close the lid of the macbook pro the monitor shuts down too. other times i'll close the lid and the monitor will keep the computer running with the lid shut and just mirror what should be on the notebook. how do i control this? usually when i close the lid i'd like the computer to sleep, but other times i like having the lid shut and the computer still running. thanks for your help!!