Originally Posted by sids1045

Usually on the top row of keys (the function keys) you see icons in color, which are functions that are activated by holding down the Fn (function) key and pressing the key you need. There should be one with an icon that looks like a monitor. (On HP laptops, it's Fn+F4, but if it's not an HP you'll have to either look for the monitor icon or...gasp...RTFM.) You can't do this using remote access (like LogMeIn, VNC, etc.). You have to press the right keys on the laptop's keyboard.

Typically the monitor function key toggles in sequence:
--Laptop monitor only
--Both monitors
--External monitor only