Different types of sites require different types of advertising, post your site so we can get more of an idea.
This isn't really advertising but it helps. Start of with less boards, so it looks like your forum is more active. You have a few boards there with only 1 post in them, which makes it look inactive so people won't want to join.
Also make your site look better. Is it a custom board? If so maybe get someone to make a cool skin for you if you can't.
I agree with the less boards. Also, have you considered concentrating on a single theme or topic? That way you have something that can attract a nucleous of people interested in the same thing. If it branches off into other things, great.
It just seems everyone and their brother has a forum just about whatever.
Think about the forums you participate in. Why did you join?
And, not trying to bust your bubble, but forums and boards are notoriously the WORST place to put ads. I know a owner of a very popular forum who told me nothing is more frustrating to have 20,000 page views in a day, without a single click. It seems posters get oblivious to the ads around a forum. Of course there are exceptions.
On any account, Good luck!