If you have been sitting in front of your computer for an hour and still have no idea how to start your story, then stop, distract your attention and read something useful. Many famous authors have own blogs and books about writing. Read their recipes of success.
Do not try to write a saga at once. Start with a small story or a poem. Take it as a spade-work, perfect your writing skill. Do not worry about the quality at this stage. First, write your small work, put it away for a while, and then read it. You will be surprised how differently it will sound after a couple of days. You will see the defects that you have not noticed at once and will look at the work from another point of view.
Beginners should do some short writing exercises. Do it every day, because writing is like training muscles: the more you train, the stronger you become. Also you should keep your notebook close at hand, in case if a great idea suddenly comes to your head. Be an observer and make notes.
Do not forget that you write for own pleasure. If it is not about you, than probably the subject is totally not of your interest or you just need a break. Turn out such thoughts as "writing is not my vocation" or "a child could write better than me".
Put aside this story and start writing something new, just for fun. Complete a small work - something that you will totally approve. In such a way you will prepare yourself for writing a longer story.