Sheeshshe- have you tried a broad spectrum antibiotic? There are viruses out there that can do the dangdest things to chickens. Wild birds will carry who knows what in and all it takes is that one with the funny mutation of whatever to completely stump everyone. Or one or two birds in your flock who are particularly vulnerable for whatever reason. Had that happen to my polish. She refused to eat and got this neurotic tic where she'd rub her face on the floor for hours. He comb started bleeding she was rubbing so much. She couldn't walk either. We treated her and hand fed her baby bird food for a week and she improved but the brain damage was permanent and we ended up having to put her down. Vet never did figure out what it was. And it was an avian specialist too, so...