How to Start

I have been trying to write the same story since I was in the third grade. Of a girl who struggles and falls. Of her friends and family. Of the different ways each character is amazing. I have written and rewritten this book so many times, but I never finish it. I always get stuck at the beginning. How to start? Is it when everything is happy or when the worst was over? Do I start when they have nothing or show when they had everything? I want them to be happy. Its why I don't read the last book of a series. My burning need to know how it all ends is replaced by my fear that they won't be happy. That the series will end with all those people, I came to love being unable to piece themselves back together. So, where do I start? When their family was in pieces? When they could not see past their pain? I could have the whole story to be about how they came back together. Or would the story be all about how they fell apart?