This procedure applies when two or more monitors are connected to one computer.
Open Display in Control Panel.
On the Settings tab, click the monitor icon that represents the monitor you want to use in addition to your primary monitor.
Select the Extend my Windows desktop onto this monitor check box.
To open Display, click Start, click Control Panel, click Appearance and Themes, and then click Display.
Selecting the Extend my Windows desktop onto this monitor check box allows you to drag items across your screen onto alternate monitors.
Or, you can resize a window to stretch it across more than one monitor.
Install additional monitors
Move items between monitors
Arrange multiple monitors
Change the primary monitor
Multiple monitors overview