I have a 21" Dell CRT monitor. About a third of the way from the top
of the screen there is a horizontal line - just like you see when an
entire line of pixels fails on an LCD monitor. It's only very faint
at the moment. The line is dead still (doesn't roll with the refresh
rate) and it is (obviously) more noticeable when the screen is white
or the white mouse pointer is positioned so the line passes through
it.

What would cause this kind of fault !?

Allan.