How do you deal with a friend who is mad at you but won't tell why?

Rather than creating more drama, put the friend on the spot. If they do not say, then you have no obligation to guess, figure out, or investigate just what it is that they are mad about. Sometimes, it is just passive aggressive: you did this to me and you know what you did. It is painful for you, but really there is nothing you can do about it.

Well at the moment I am having the same problem. My friend has said to my other friend that she doesn't want me to sit and hang out with her group anymore. And my friend is saying that I'm taking her place in the group and I know secrets she doesn't which isn't true... things like that. I would try and sort this out but she is giving me the 'silent treatment' and won't talk to me.

My answer to you is maybe get one of your other friends to ask her/him why her/him is angry with you and if your friend tells them why, then get that person to tell you. (if that makes sence. See if your friend will talk about it. Hopefully your friend is willing to sort your problem out.

If this doesn't work then I'm not sure.

Hope this helps! :)