But it was not a monitor issue but a video driver issue. As no OS or host PC is noted, I will guess badly you have a Dell PC. Use your service tag to go to Dell.com and get the video driver for your PC and install it.
I have been getting black squares on the monitor which disappear when I click in a different spot. This only happens when I am online. I have looked all over and the instructions I have found are:
1. Close all open programs.
2. Click Start, and then click Control Panel.
3. In the Control Panel window, click Appearance and Themes, and then click Display.
4. In the Display Properties window, click the Settings tab.
5. Click to select the color depth you want from the drop-down menu under Colors.
However, there is no "Appearance and Themes" in the Control Panel, and there is no drop-down menu under Colors when I access the display using Settings.. I have also tried the buttons on the monitor.
I'm running Win 10 64-bit and primarily use Chrome. But I also tried Mozilla and had the same problem. Problem is intermittent.

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