Left click in the area just to the right of Start and drag the bar back from
the right side to the bottom.  Once it gets back into position, right click
on it and then click Lock the Taskbar.  This will help in preventing the
movement in the future.

Press/hold down the left mouse button on an empty area of the taskbar.
Drag the bar back to the bottom of the screen.  You won't actually see it being
dragged, it will snap into place when you get near to the bottom edge of the
screen.
Once the taskbar is back where you want it, Right click an empty area and click
"Lock the taskbar" in the popup menu.

1) Unlock the TaskBar (place the mouse cursor on any empty space on
the TaskBar, and right-click on it.  A menu will popup: Click on "Lock
Taskbar" if there is a checkmark beside it. If there is none, go on to
step 2.)
2) Once the Taskbar is unlocked, move the mouse cursor anywhere to the
right of the last icon (NOT In the QuickLaunch, however), and press
and hold the left mouse button, and drag the TaskBar back to the
bottom of the screen.
3) Relock the Taskbar if it is still unlocked.

Then you should set a local policy to disallow the unlocking of the
Taskbar by anyone but yourself.

But that's a horse of another color...

Donald L McDaniel
Please reply to the correct thread and article.
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First, note that it's called the Task Bar, not the Start Bar.

Although by default the task bar appears on the bottom of the screen,
it can be on any of the sides you prefer it on. To move it from any
side to another, simply click on an unused part of it and drag it
where you want it. Be sure to click *within* it, not on the edge;
clicking on the edge and dragging will resize it.

If it won't move, it may be locked. In that case, right click on it
and uncheck "Lock the taskbar," then try again.