Here's a great The Journeyman Writer podcast from StoryWonk about what to write when you don't have an idea. It also touches on what to do when you feel your story idea has been done before (hint: write it anyhow!). It's a perfect subject right before NaNoWriMo.
I think we get hung up sometimes on wanting to write something that's never been done before (that will happen because you have never told this story before, so stop worrying about it!) And we get hung up sometimes on thinking we should do something different. "I love ghost stories, but my last three stories were about ghosts so I should do something different." Write your story. Write what you want. Get a little inspiration from this podcast then go get some words down.