If I didn't have a story idea... what might I do to come up with one? Hmmmm.
* Newspapers would be a good source for inspiration, though I've personally gotten very little from them, myself.
* I pay close attention to my dreams at night... if I was sufficiently entertained or frightened, I may explore that as a potential story, scene, etc.
* You might start by exploring some "what if's"... centered around themes like: What would utterly break my heart right now? What would scare the crap out of me?
* Don't be afraid to use those you know as a basis for your characters.
* Also, if you are writing the story, because you want to film it yourself... be sure to write within your budget, using the resources you already have at your disposal. This may seem limiting, but you may be surprised at how creative it actually makes you, when you have to concoct an interesting story that takes place in your bedroom (the non-pornographic kind, I'd hope).
I hope that helps. I don't know of software or books to help you COME UP WITH a story. Only to flesh them out.... aside from books that list a million different plot set-ups and themes. Those might get your started. Look on Amazon.
I have a half dozen note pads around my house that are used constantly. I always bring a small one and a pen with me when I am out. Write down dreams. If you use public transit it is a good way to "overhear" funny stories or ideas that can be used.
I try and put all notations into a basket where in a day or two I will go through them all and type them out and sort them into other notes I have been taking for the past year or so. Once you have been doing this for a while, organization becomes a huge factor, so do it from the beginning.