Hi... as Michael said, this bird was probably hand raised and then not interacted with once weaned. Some birds revert quickly to being skittish after some time not being handled. Ringnecks are one that will go wild more quickly than others.
I didn't read the entire thread but I'm going to offer advice anyway. Hope this hasn't already been said.
First, never, never force the bird out of his cage. This will only make him scared of you. You want him to trust you. (Lots of people will argue with me but I'm just going to have to say that I'm right on this one. ) You were doing everything perfectly to start with. Sit by the cage and talk to him, sing to him, whatever. You'll be able to tell when he is paying attention. Offer him treats through the bars. Start using your bridge for future training whenever he takes a treat from your hand. For instance, you offer a nut, he takes it, as soon as he takes it say "good!" or use your clicker or whatever your bridge is. Be consistent with this. He will start to associate the bridge word with happiness (his treat) Leave the cage door open all of the time when you are home. Put some of his favorite treats outside of the cage to entice him. Eventually he will start coming out on his own. Once he does, let him sit on top of his cage, or where ever he wants, and talk to him etc as you were doing through the cage bars. Don't try to force him to step up yet. Let him get comfortable outside of the cage. Put some toys out... maybe he'll start playing. After he seems somewhat comfortable, then I'd start trying to train him with the step ups. I think Micheal posted a good tutorial for teaching step ups? You don't have to use a clicker as the bridge... you could use a word. I personally use the word "good" as a bridge but that's personal preference. It will take lots of patience but you can succeed! Don't give up on him. If you gain his trust you will have a friend who adores you for the next 30+ years! Ringnecks can be good little talkers too. He is young so it shouldn't be too hard to gain his trust. Good luck! With patience and persistence, you'll soon have one of these adorable little birds...