Not being able to lift the head could be anything from poisoning such as Botulism, a severe neurological problem from an injury to bad bacterial, fungal or viral infection or a nutritional problem. The bird needs to be seen immediately by a bird veterinarian for proper diagnosis and treatment. If it is not eating, this is, already a bad sign and the bird will die soon. The bird veterinarian will know how to tube feed it, but even now, that may be too late. Please get the swan to a veterinarian immediately. The Regal Swan