the home sharing doesn't work between my apple tv and windows computer

I have already set up the home sharing both on my apple tv 3 and my windows computer.And i'm sure they 're in the same network.But i can't visit the itunes library on the apple tv 3 through the home sharing.the apple tv asks me to set up the home sharing on my compter,but i have already done that.i don' t know what to do.