First of all, does your site justify a forum? There had to be a reason for you starting a forum, what was it?
Unfortunately many boards end up this way. Many think that a forum is a great way to bring in visitors. That is not always the case.
Usually when a forum is considered, it is because there is a history behind the site. That history is a telltale sign of whether or not a forum would be successful. If your site does not justify a forum, don't waste your time.