Marcel, place your mouse pointer on the bottom edge of the tool bar. It will change to a double pointed line. Press the left mouse button and hold, drag down until the tool bar is half the screen wide. Release the mouse button.
Now place the mouse in the tool bar about mid way, press the left mouse button and hold. Drag your mouse to the left and the bar should move to the left side of the screen. Release the button and repeat, except this time drag the bar to the bottom of the screen. Now the bar should be back on the bottom.
Move the mouse pointer over the top of the bar until you get the double pointed line, left click, hold and drag toward the bottom of the screen to reduce the size of the bar.
Now that it is back in place, place the mouse pointer in the bar and right click. In the screen that pops up, select Lock Taskbar. It shouldn't move on you again.