Absolutely go back to the beginning. Whatever scared him, and you may never really know what it was, he needs to be treated as a brand new hammy and you have to build up trust again. I'd leave him be, except for watering and feeding him, softly talking as you do this, for about two days, then begin again using soft talking when you approach his cage, have tasty treats so he attaches good thing to your arriving at his cage and allow him all the time he needs to re-establish a relationship. He'll turn around again. Sometimes something we don't even think about can upset these little furries. Good luck with him
LOL The playpen is great! Ted E Loves his.