I need help writing a novel....?

I am extremely introverted, I'm also a chronic daydreamer sometimes losing whole weekends to day dreaming, as a result I have all these worlds and stories, that I know would put most movie makers to shame, I'm not bragging, I have been living in fantasy worlds since I was 12 years old. Some of my fantasies(they're not ual) have been repeated and refined in my head over years and years. Yet when I got to put them on paper I freeze, I don't know where to start, my mind goes blank, I'm not looking to get rich, I just want to share these Amazing stories and scenarios I have in my head. Anything would be helpful, I've tried the basic stuff, writing diagrams, flowcharts, pictures, switching to typing from writing, any advice would be welcome. Thanks to all of you who take the time to answer.