Have you run the Dell Diagnostics?
Any errors in the device manager?
Are you able to adjust your screen resolution?
Double check you Quick Set settings.
Is the ALS enabled or disabled? Check to see what is it set at.
This screen you are referring to is your LCD and you have the Power Supply adapter plugged in, not an external monitor right?
Here is a link to the owners manual:
http://support.dell.com/support/edoc...n/ug/index.htm
Thanks,
Bill