This happens if you use "Slow" bulbs on top and you have Microsoft's Active Desktop set to "View as Web Page".

Unless you're actually viewing a Web page as your desktop background, you probably don't need to have it set that way. You can turn off the Active Desktop feature, and even though your desktop will look the same, the flashing will stop.

To do this:

1. Click the Windows Start button.
2. Choose Settings.
3. Choose Active Desktop.
4. Choose View as Web Page so that the checkmark disappears.