I would plug in my external monitor via the vga cable and it would instantly show. Now my host laptop screen when plugged into the external monitor goes black.
I have tried turning each off and starting in succession but no - whenever the external monitor is plugged in, my laptop loses screen but the external monitor shows a mirror image of my desktop with mouse moving etc and is ok.
Took the host laptop out for a walk and used it for a PP on an office projector and it worked fine - no black out screen. Gets it back home and plugs it into the external monitor that gave the problem in the first place and nothing has changed. As soon as the plug enters the laptop the screen goes black but on external monitor all is normal looking.
HP Laptop running Windows Vista Home Edition