I just purchased a Dell P2210 LCD monitor and attached it to my MBP using the DVI cable. Everything looks good on the external monitor but when I try to view both the external and internal laptop, the laptop screen is completely black/blank. I've arranged the windows in the Display sys preferences to be side-by-side and I can drag a window to the blank internal monitor but it doesn't show up there. I've tried many different resolution settings and nothing works. Does...