Decline in activity? That could be due to a number of reasons like the layout (it is rather outdated and looks as if it was created during the first years of the www), too many forums, less topics being posted in, for one there are topics ranged 120 days older on some of the pages. That signals that no one is hardly ever on the site. This site needs to revamp itself with a proper lay-out that would attract students to the board and possible get some features. I hear VBulletin is a nice design for forums. TLS has a better layout but that layout is a basic phpbb layout and does not really attract users.
Yes, this is good for users getting information, but users need some more incentive to come back. New features, better design, diminish some of the forums that are inactive, get rid of the black based forum as it is a form of discrimination, get rid of the AA forum as that too is a form of discrimination. If you want to purport equality, make things equal. I do not believe it is fair for any race to have a forum designated towards just once group of people. It actually hurts that group of people and promote racist notions, rather than help them.
Get some content on the main site: [Example of the content layout your main site could use to look more professional].http://files.vbulletin.com/images/cart/screenshots/CMS_home.png
Get a better forum layout and design: [Example of how your forums could be used to attract new members]. http://files.vbulletin.com/images/cart/screenshots/forum_main.pnghttp://files.vbulletin.com/images/cart/screenshots/vertical.pnghttp://files.vbulletin.com/images/cart/screenshots/horizontal.png
Member profile pages: [Adds some appeal different from other sites like this one]. http://files.vbulletin.com/images/cart/screenshots/member_profile.png
Not only that VB also has blogs integration and a bunch of other user-friendly features. It only costs around $285/suit but if you are only needing one then $285 is the price. I say it is worth it as you have to put effort and a bit of money into running a successful site. Ways you can get the money is through donations and I'd be willing to donate as I view this site as something useful.