I updated/re-installed some drivers (one at a time followed by a full Windows start-up and shutdown to check if the problem was still there), and found out a corrupt graphics driver was causing the problem.
Indeed... that is the correct course of action... methodically doing stuff one step at a time and, in the case of configuration settings (rather than drivers), changing settings back every time before changing new settings.
So if PPRuNe Pop is willing to put in the time, then I'd start by ruling out hardware issues, then updating drivers one by one, then finally start fiddling with configuration settings.
If all that seems like too much hard work, then see my "easy answer" above.
Could be anything though! Good luck.
I second that statement !