I have had a similar problem – when I installed BBPress on my WP site, I suddenly lost the ability to edit or delete existing posts, and EVERY page and post in my site (all Public pages) result in a 404 error except when you’re logged in as a member. As I installed BB with the intent of an integration, all the BB tables went straight into the existing WP database, I am assuming my problem lies in a new column within the wp_posts table called “forum_id”.
I was also hesitant about editing the DB, though, as I didn’t know a whole lot about it. Would also assume that the tables with prefix wp_forums are the ones generated by BB…is this right? Can someone give me some idea of how to fix this, as it is a really serious problem and has basically disabled the whole site (even the home page can not be viewed by non-members).