When he was a puppy...was he the same way? He might just be having a hard time adjusting to everything and very unsure of it. That might be part of the reason but just give him more time to adjust. When we brought Lizzy home it took her a week to go down the stairs herself. She was even iffy about the grass for a day!.. same with the carpet.. and the tile... just give him time. Lizzy at first only went down the stairs when we weren't watching. She also didn't eat much at first. I'm guessing everything is a big shock and adjustment for him.. just make him feel like he is loved and at home. keep trying and if it continues post back.