you keep telling me the adapter is unknown but it is a dell adapter bought with the computer

dale palmer, July 2011

The connector on the Dell charger has 3 electrical connections, +, -, ID.

The ID connection fails because of a fault either with the charger or the Laptop so the Laptop no longer recognizes the charger so won't allow a charge cycle to start.

This generally is not a DIY repair, you need professional help but don't go to Dell as they charge an absolute fortune.

Computer Dave, May 2014