Oh I don't know... "read directions" comes to mind. Not trying to be a
smart alec but often we overlook the resources already at our fingertips -
help files, manuals and the like. Since systems can vary so much, those
resource are the most accurate for *your* system.
NOTE: There may be a utility separate from display properties that is to be
used for enabling the external monitor. For example, there is a tray icon
on my portable system that enables and manages different display
configurations.
