Ok, I don't know whether this is going to help or not but I managed to recreate your problem by dragging the generated media window out of sight below the taskbar. It all depends how far down it is.

I managed to recover it by setting the windows taskbar to auto-hide. I could then see the very top of the hidden window. By moving the mouse down very slowly and carefully, I managed to get the cursor to change to the "resize window" cursor before the taskbar reappeared. I then dragged the cursor upwards, resizing the window until it was properly back in view and could then be moved.

EDIT: Actually if you uncheck "Keep taskbar on top of other windows" (right-click on taskbar + properties) that will probably make it easier as well.