What do you do when a friend stops talking to you..

and will not tell you why

That's a hard one. I'd be tempted to ask around to see if any other friends know anything.

Let's hope she will give you a chance again--or at least tell you why she isn't talking to you anymore at some point.

I've been there. I chased answers for a long time. I was depressed, cried a lot, asked mutual friends what was going on but she lied to them and said everything was fine. I had to finally let her go so I could move on with my healing. I still to this day get anxious when I see her at a mutual friend's gatherings.

Over the years I've done a lot of reflecting and have come up with a couple theories that make sense to me, but will never know for sure. It really tore me up for a long time, and would have continued to do so had I not let her go.

In your case maybe it's not as severe. Perhaps give her some space and try again, let her know you want to make things better but cannot do so unless she tells you why she is upset, but recognize there may come a time when you have to move on. (It took me years to get there if I remember correctly).

Good luck with your friend, and I'm sorry.

Why not just ask your friend if you have done anything to offend he or she and see what your friend says. Don't reck your brain trying to find out for yourself or asking others I say go to the source itself. Hope all works out for you friend.

I guess you grieve. It has happened to me, it was really uncalled for and very hard.
I had to let go of the friendship. A whole year passed in silence when out of the blue the contact started up again and it started with an apology but no real explanation.

I didn't push it and now keep my distance & keep any contact light. No use rolling into another train wreck for no reason.
You live you learn & you protect yourself.

Sorry for the hurt...