I allow my desktop to go to sleep overnight, and the monitor turns itself off. In the morning, when I wake the computer and monitor, there is a dark, triangular dark area (like a shadow) in the lower right corner. It takes up about 20% of the screen. I find that if I allow the monitor to display for several minutes, then turn it off for a few minutes, then turn it back on, the dark shadow is gone and the display is fine for the rest of the day.
The image on the screen is visible 'behind' the shadow area, and the cursor is active there also. The size of the dark area varies somewhat, sometimes a bit smaller.
This behavior started a few months ago.
At the moment it is only a nuisance, but wondering if something is failing after 3+ years of use.
I understand the monitor screen turns the dark area in the lower right corner after overnight sleep.
Don't worry I will try to help you out.
Did you make any changes to your monitor?
How is the monitor connected from your PC?
Have you tried connecting the monitor to a different PC? Does the issue persist?
Have you tried checking with different video cables?
Press the Auto or Autoselect button on the display.
Press Menu, and select Factory Reset.
If the display has more than one type of connection available such as VGA, DVI, or HDMI, try a different type of connection.
Set the video resolution on the computer to match the native resolution of the display. Find the native resolution for your display from the box the display came in, the Monitor User Guide, or product specifications. To change the display resolution, use the following steps:
In Windows 8, press the Windows key + X key, click Control Panel, find the Appearance and Personalization area, and then click Adjust Screen Resolution.
In Windows 7, click Start, click Control Panel, and click Adjust Screen Resolution in Appearance and Personalization.
Move the slider bar until the native resolution for the display is set, and click OK.
If the native display resolution is not one of the settings that you can select or the problem continues, continue to the next step.
Refer this article to further troubleshoot display issues with your monitor.
If the issue still persists after trying out the steps it is a hardware issue with your monitor.