I hesitated to answer, because all I have is some speculation. Since no one else answered, I'll give you my theory:
I've had this happen occasionally when running older computers at the highest screen resolution they were capable of. It only happened occasionally and seldom took more than one re-boot to fix, so I didn't try to do anything about it....
My opinion was that it happened because I was pushing the limits of what my video card and monitor were able to do, and sometimes something was less than perfect.
Experiment:
Right-click on the desktop and select "Properties".
Click on the "settings" tab:Let us know if it works out. I'm curious.
- Try lowering the screen resolution (Screen Area) and see if that helps.
If not also try lowering the Colors setting (bits).