You don't have to physically disconnect any of your displays to turn off the multiple monitors feature. With Windows 7, you can access your display settings through the control panel to quickly turn monitors on and off. In the "Display Settings" window, there are on-screen representations of your monitors. Windows automatically assigns each monitor a number, so it's easy to distinguish between monitors and select the ones you want to turn off.
Click the "Start" button on the taskbar.
Double-click on "Control Panel" from the pop-up menu. The control panel window will open.
Click "Appearance and Personalization," then select "Adjust Screen Resolution." A new window will open.
Click the drop-down arrow in the "Multiple Displays" field. Select one of the "Show Desktop Only On..." options. This action will turn off the other monitors currently connected to your computer. For example, if you have two monitors attached to your PC, and you select the "Show Desktop Only On 1" option, Windows will turn off monitor 2.
Click "OK" to save and exit.