External Display

>I tried to connect my laptop to my HDTV through a VGA cable. It recognized
>it
> at first and on my pc a alert box popped up asking if I wanted a mirrored
> display, an extended display, or external only. I hit external only and
> then
> clicked apply. I flip through the different outputs on the TV and come to
> PC
> and get a message saying "Not Supported Mode." Since I hit that every time
> I
> plug the VGA cable into my TV and PC at the same time my PC screen goes
> black
> because its supposed to be external only and for some reason it doesn't
> support it. I want to try and change the setting fer this external display
> to
> mirrored but I can't find a way to do it when it isn't connected and when
> it
> is connected I can't see anything either because the PC screen shuts off
> and
> the TV won't display it...What can I do to change it. I went into the help
> and support thing on my PC but the only way it's giving me is if it's
> connected in which case I can't see anything...any help would b
> appreciated.