Open Screen Resolution by clicking the Start button, clicking Control Panel, and then, under Appearance and Personalization, clicking Adjust screen resolution.
Click the drop-down list next to Multiple displays, click Extend these displays, and then click OK.
If you don't see an option named Multiple displays in your display settings, then Windows isn't detecting a second monitor plugged into your desktop computer. Or, it is not detecting an external monitor plugged into your laptop. When Windows detects this monitor, it will appear in the drop-down list next to Display. If you don't see it listed there, try clicking Detect.
Make sure the monitor you want to extend your desktop to is turned on and plugged into the correct video port on your computer. You might also need to select the correct source labeled on your monitor's controls to ensure the monitor is using the correct video port. For more information, check the manual for your monitor or go to the manufacturer's website.