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I have thought that why need dual display/monitor?
But mow, I think dual display/monitor is very usefull.
1.Check the graphics card of the PC
First、you need to check graphics card of your PC if it supports dual display/monitor or not.
If your PC do not have support, there is a way to replace the graphics card,or buy a new PC.
2.Check terminal to connect the display/second monitor to your PC.
Let's examine whether or not there is a terminal "D-Snb/HDMI" to output a video display/monitor to the computer. Your PC do not have a terminal connected?There is a goods that converting to USB port are selling.
StarTech.com USB to VGA Multi Monitor External Video Card Adapter - 1440x900 - USB to VGA External Graphics Card
3.Check display/second monitor is what corresponds to one of the analog/digital?
Before you have a display/second monitor, to put them in either digital or analog ,check the display/second monitor.
Connection terminal of analog and digital from the computer is different.。
Analog cable is generally,C2G / Cables to Go 45138 Ultima HD15 Male/Male SVGA Video Cable (6 Feet/1.82 Meters),and Digital cable isAmazonBasics High-Speed HDMI Cable (3 Feet/0.9 Meter) - Supports Ethernet, 3D, and Audio Return [Newest Standard]
4.Is there a place to take a power supply to the monitor?
If the display/second monitor is not a built-in power supply, of course, power supply is required.
It would help to check the power strip is not full.
5.After you connect the display/second monitor ...?
After you connect the display/second monitor, let's settings.
For example, you may need to install the driver first.
In addition, in the case of the windows7,
「right-click any empty area of the desktop > Screen resolution」
it is on the screen, such as the image below.
Select as a display/monitor the main display/monitor either 1 or 2,and select「Extend these displays」,apply ＞ ＯＫ. Now setup is complete
By the way, you can also switch between dual display/monitor, such as the image below in the shortcut of "windows key + P" (windows8 also like this) in the case of windows7. It is convenient.