change display setting to extended ( setting dual screen)

1) open screen resolution ( start - control panel - Appearance and Personalization click adjust screen resolution)

2) Click on multiple displays - click on extend these displays and then APPLY and OK...

p/s :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,and Make sure the monitor you want to extend your desktop to is turned on and plugged into the correct video port on your computer