[xubuntu-users] trouble changing monitor

[amckeag at blueyonder.co.uk]

hello.
please forgive me if this is a very basic silly question :) i hope one of
you out there can help me.
my monitor appears to be dying..the picture shrinks from the top and
bottom of the screen into a thin line running straight across the centre
so most of the time it is unusable.
i unplugged it and tried to plug another smaller monitor in. it started up
normally and reached the black screen just before the blue xubuntu log in
screen appears. the blue screen never appeared. it remained on the black
screen and the monitor's LED power light changed from green to a yellow
blinking light. is there a special way to change monitors that i'm not
aware of? i've obviously done something wrong..

thank you

am