Carolina,
Hold down the control key and drag with the existing guide. Drag as far as
you want the guide to be and release your mouse. If you hold the shift key
as well whilst dragging you can start from 0.
The maximum is 8 guides horizontally and vertically.
Never heard of a locked guide yet, maybe you are not seeing the guides but
the grid instead. You can access the grid by clicking on Draw - Guides and
grid of the drawing toolbar. Or maybe the lines you see are just lines that
have been drawn using the drawing toolbar.
