If it's writer's block about starting a new story with a new idea...can't help you there. I've gone more than a year without writing a single story. If you've already started a story, here's my advice...
Delete the last chapter or two that you've written and rewrite them. Sometimes you'll find that you've written yourself into a corner that your mind won't let you out of, and if you try it again from a new perspective, things might work better.
Brainstorm with other people for ideas. Go on irc to #loisclark or #lanekent and find someone willing to listen and comment. Use a beta reader to bounce ideas off of.
If that doesn't work, then try to remember what got you excited enough to write the story in the first place. Even if it was a school paper or article, what made you choose this topic over something else?
Remember the theme...what are you trying to say through the story?
Just some random thoughts...hope they help.
