The Windows operating system designates your single and only monitor screen as the primary display on the PC. However, computer manufacturing companies are increasingly building desktops and laptops with extra display capabilities. You can connect a second larger, better-quality LCD monitor to replace an existing PC display or share the screen across both monitors. Some PCs also connect to flat screen plasma and 3D television sets. After you have connected your PC to the another hardware display device, per manufacturer instructions, you will need to perform a software change in Windows to complete the process of reassigning the primary display.
Click the circular "Windows" orb logo in the bottom-left corner of the desktop (also known as the "Start" button). Type "Display Adapter" in the search box at the bottom of the "Start" menu. Press "Enter" to open the "Display: Screen Resolution" window
Open the drop-down menu next to "Display." Select the name of the alternate display adaptor that will become the primary adaptor. Windows usually identifies the secondary adaptor with the number "2."
Check the box next to "Make This My Main Display."
Click "Apply" and "OK" to change the secondary display adaptor to the primary display adaptor.
Press the "Windows logo" and letter "P" keys on the keyboard to bring up a display dialogue box. From this menu, choose to duplicate the display on both monitors or extend the display across both monitors. The logo key is between the "Ctrl" and "Alt" keys at the bottom of the keyboard.
The option to change the primary adaptor will not appear if Windows only detects one "display adaptor."