After having my initial server crash, I built a new one and copied all configuration and related databases over. I can see the forums, but I cannot get to them. (Clicking on the forums link brings up a list of the forums, but clicking on a specific forum won't bring up the topics in that forum.) I don't see any errors in the httpd (apache) logs.

Where do I start?

Thanks,

Did you remember to copy the forum templates into your theme directory?

Yes, it's there (/var/www/html/layout/professional/forum).

Best start here: http://www.geeklog.net/faqman/index.php?op=view&t=37