Tony,
If you have a very complex object or many objects in a scene, sometimes
the redraw rate for each window (top,front, side) is very slow. In order
to get around waiting for the windows to redraw before the perspective
view redraws or access to the menus options, etc., the ESC key can be hit
which aborts the redraw. This is especially useful if you are trying to
move to a specific location and you don't feel like waiting each time you
hit the left,right,up or down arrows.
Alan Henry