Windows Updates often include unnecessary driver updates for some reason, an update to the Graphics Driver could cause this.
I thin k you are right. It is a Intel chip in a stock Dell desktop, a 745.
A few weeks ago it was working. There is no rollback.
It is possible to go into the display settings and force it in the other position, but that is awkward. You can not just flip it aback with hot key.
Oh well, another reason to finish my transition to Windows 7.
By the time I get there, Windows 7 will be at end of life!