My S40 diesel has elecrtic power steering, so does not run off the engine belts (this is supposed to improve fuel economy) so as 7050man said, looks like the electric motor has died, or the connections to it have passed away somewhere. I wonder where the system gets its input from, and also where it gets its feedback? I'd be tempted to have a grovvel round under the car with the undertray off and look for loose, disconnected. chaffed wiring etc.