I will start any video games. They are almost always in fullscreen or windowed fullscreen. Mostly later because I can alt+tab and look up meta-game info when necessary.
Ever since the windows 10 update like 3 or 4 weeks ago. I don't remember exactly when.
The problem started and there seem to be no sure fire way to fix this. Restart might resolve the issue for a little while before coming back. Alt+tab just move the window down and right as expect then back to the same issue again.
I can't be 100% sure where the cause is. But I strongly suspect it has to do with my old PC and how it interact with windows 10/current nvidia driver.
Now the issue is that the windows task bar that normally would disappear if I have a fullscreen application running will NOT hide. Instead it will treat the taskbar as click for taskbar instead of the fullscreen. It also block some button/info on the bottom which makes it impossible to play certain games that may depend on the area behind the task bar.
Here is an example screenshot from Dawn of War 3. IGNORE the low quality graphic I was just testing the tutorial and see if it runs at all.
That said there are plenty of games that will not suffer from it at all while other do.
My setup is black 1075t amd cpu. Nvidia 660 GTX.