Here is a list of steps you can take to troubleshoot why your desktop wallpaper is not displaying:

1. Check that your display settings are correctly set.
2. Check that the image that you are trying to set as the background is also correctly formatted.
3. Check if there's an issue with the video driver.
4. Check if there's an issue with the wallpaper file.
5. If the above steps do not work, try restarting your computer or resetting it to factory settings.