What would cause water to not fill the tank. The water handle is on and the toilet flushes if I put water in the tank, but it will not fill on it 's on. The toilet is only 1 year old.

What would cause water to not fill the tank. The water handle is on and the toilet flushes if I put water in the tank, but it will not fill on it 's on. The toilet is only 1 year old.
What type of ball cock do you have? A float ball on a rod or a can on a wire,(see images)? Regards, Tom