Is it possible you could do a screenshot of it and show us? Or if it doesnt show up in that, maybe a picture on a cellphone or some other method? It would help to really narrow down what you are talking about.
As for the actual problem, check something for me:
Right-Click your taskbar
Click Properties
Ensure the box that says "Auto-hide the taskbar" is checked
If it is, then what i'm thinking might be the issue is in fact not it. If it is not already checked, check it then test it in game.
And, of course, do all that other usual hoohah and whatnot (drivers, updates, clean install, the fun things that never work).