[Help] New rescue extremely fearful. How do I help him gain confidence?

I adopted a 4 year old rescue dog, Nicolas, who has been living with me for 10 days now. He grew up at the shelter, and is extremely fearful of everything. He has spent the entire time since he arrived lying in one corner of his room. He's so afraid of being outside that I have to carry him out there (which isn't easy, he's a 60+ lb dog!), and then he's visibly trembling the entire time until he's back in his room.He likes treats but won't come to me for them. He won't take them if he's scared, so I can't reward him for coming outside until we're back inside. He doesn't know what toys are, and won't touch any of them.I feel like I've looked at every page on the internet about how to work with fearful dogs, but none of them address dogs like Nicolas. Many have said to take them for walks and exercise them, but the entire time we're outside he's pulling to go back in. I feel bad even forcing him to go outside when he's clearly nervous, but he won't go to the bathroom inside. He won't chase a ball. He doesn't understand what a dog bed is and lies on the hard floor. He doesn't even stand up except to eat and drink. I know it's only been 10 days but I'm so sad seeing him like this. I just want him to be happy. It kills me to see other dogs playing outside when all he'll do is lie on the floor doing nothing day in and day out. Any suggestions would be appreciated. via /r/dogs http://ift.tt/2somAGa