To detect a second monitor manually on Windows 10, use these steps:
1. Open Settings.
2. Click on System.
3. Click on Display.
4. Under the "Multiple displays" section, click the Detect button to connect to the external monitor.
How to fix second monitor not detected on Windows 10 www.windowscentral.com > Help & How To > Windows
Making sure you're running the latest graphics drivers for your system can sometimes fix problems with no signal errors. If you're still having trouble with your extended desktop monitor, verify that it works by unplugging the primary screen and double-checking the above steps again.
The Most Common Multi-Monitor Problems and How to Fix Them
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Set up dual monitors on Windows 10
1. Select Start > Settings > System > Display. ...
2. In the Multiple displays section, select an option from the list to determine how your desktop will display across your screens.
3. Once you've selected what you see on your displays, select Keep changes.
Set up dual monitors on Windows 10 - Microsoft Support support.microsoft.com > en-us > windows > set-up-dual-monitors-on-wind...
Right-click on the blank area of the desktop and choose Display settings. Click Identify to show numbers on corresponding displays (1 is the primary). Click the Multiple display drop-down list, and then select Extend these displays. Once done, restart your device to apply the changes and check if the issue persists.
Windows 10 stopped detecting 2nd monitor - Microsoft Community
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