External Monitor on Laptop

I am using an external monitor through the VGA port on my laptop. When I
close my laptop lid, the external monitor's resolution goes down to 1024 x
768. I looked in the Mobility center, and it says that there is no external
monitor connected (when the lid is shut). Is there a registry value or
anything like that to change this so that the laptop detects an external
monitor when the lid is closed? I tried doing the
ExtEvent_EnableAutoDisplayConfig registry value, but it didn't work. It
doesn't sound like that is my problem. Let me know. Thanks