If you haven't already, just try changing the resolution and see if the problem goes away. Also try moving the taskbar to different edges of the screen.
At that point, if it's still not working, two options: use VLC (it's awesome, but only supports one core so depending on how recent your graphics card is/how fast your processor is, you may not be able to playback 1080p smoothly.
And the other option is to install Win7, which is also awesome.
I suppose you could also try reinstalling WMP too.