I had this happen once and my solution involved unlocking the Taskbar (if locked) closing the language selector (if showing is has an icon that says something like 'En') and dragging the top one of the two borders for the Quicklaunch toolbar down to the lower part of the Taskbar.
This thread offers several solutions and one of them should work for you depending what is causing the anomaly which I have seen more than once.
Good luck!