2nd vdu plugged into laptop

[Brian Wootton]

Can anybody tell me where to go from here?
I've plugged a spare monitor into the video socket on my
laptop. When I switch on I get the boot-up script OK coming
up on the 2nd monitor, I get the blue background with
kubuntu 10.10 on  the 2nd  monitor OK, but it goes totally
blank as soon as the login window comes up on the laptop.
I've searched system settings and can find nothing to help,
doesn't mean it's not there though, knowing me.
ta muchly brian