Hi, I'm in need of a bunch of ideas

I own a graphics/chat SMF forum but it never seems to be very active. I get members signing up but they just look around and leave. Do you guys have any tips on how to keep members coming back?
I send out emails every once in a while explaining that inactive accounts will be removed in x amount of days, but I don't like to send those out to often as most people don't like these things landing in their inboxes.
I think the problem is that I keep some of graphic boards hidden to newbies so when they sign up they don't go in, snatch what they want and leave (believe me I had that problem in my last forum x_x) So maybe newbies just think there's nothing worth staying for? Should I show the graphics boards to newbies? (I just don't like the idea of people stealing other people's work xP)
Also do you guys have any ideas on rewarding the members who do post?
Any good ideas would be appreciated!
