Author: Raul Galaviz
Setting the input on a Dell All-In-One (AIO) to use as a second monitor
1. Locate the 4 buttons on the side of the monitor.
The bottom button is the power button. It is separated from the other 3 buttons.
The top 2 are brightness control buttons and selection buttons, the third is the input button.
2. Power on the computer, then the monitor. Then press the input button and you should see this:
3. Press the corresponding side button to select the input button 
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4. Different input options will be displayed, VGA, HDMI, Computer and Composite.
5. Using the top 2 side buttons, select an input, either VGA or HDMI.
6. Once selected, the monitor should display your desktop.