On second thought, perhaps my advice was a bit trite. I well remember sitting down to write my first stories, then not knowing what the first words should be.
If this describes your situation, try this:
Start the story with the words "There was". Write 2500 words (about 10 published pages).
After 2500 words, stop. Go outside for a walk. Play with the dog. Get a good night's sleep.
Start again. Tell the beginning of the story anew, using different words. Include new things you've thought of. Nix stuff you've decided against. Experiment. Have fun with it.
Again, after 2500 words, stop. Let it rest for the day. Sleep on it.
Do it again. This time, tighten up your writing. Eliminate unnecessary words and elements. Your 2500 words will take you farther into the story because your writing will be more compact, more precise.
Hopefully, by this time, you'll have found the thread of your story, and your story will have found its own voice.
If not, keep trying. One story took almost 40 attempts before everything clicked. When it finally did, I thought, "Why didn't I just think of that in the first place?"
Best of luck.