To me your front page looks a little confusing...almost all forums are in main category, which makes navigation very dificult. Also you should propably cut down significantly the number of forums...maybe delete all subforums, as activity tends to get lower, when there isn't any very active sections...If you get more members you can always add more folders, but imo it's better to start with few active sections instead of spesific section for every issue. You should also think about some sort of marketing plans. You could offer adsense revenue sharing, referral system, bonuses for being active (for example a text link in the front page, or active user links page) etc. Then of course you need more traffic...search for similar forums, market your forum there, exchange links with sites related to your content, stumble etc etc.
Here are a few from the top o my head - Get some regional targetted traffic - Offer more services, look at iwebtool.com - Make contests,"referral contest" for one. - Get writers and pay them for original articles.
I have had good luck with a welcome block. Something that says you need to register before posting or something along those lines! Also, PPC was the best solution for my community, also word of mouth with your friends works wonders!