How do I help my Fearful dog and Retraining.?

[Tyler]

I recently adopted a 2 year old border collie. He seems like a very smart dog but he has some issues and this is the first dog we've had. He had one accident in the house since we've had him but seems like hes doing better. When going up the stairs (outside) at my house he suddenly stops at the top of one level and crouches down and gets very scared. at this point he wont move until pulled or picked up. there are a very few times that he can overcome it with encouraging words but he also does the same thing when we try do leave through the front door or trying to get him in the car, he doesn't tug on the leash he just wont move. also coming when he has called and being obedient outside, i.e. not being on a leash and running off listening when hes called not pulling on the leash. I want to know what would be the best way to retrain the dog and if its possible as well as building confidence.