You're doing a pretty sketchy thing. You can't just plug a database into a new forum that has new files, as some of the files such as your configuration, uploads, etc, all relate to the database. Things will appear as broken, if they work at all. You could just save your posts and forums, I suppose, but I've never tried that, nor do I recommend it.
Depending on how trashed your forum is, you may just want to take this opportunity to start over. That way everything will work perfectly and any issues you're experiencing now will be squashed, versus potentially re-appearing later on. But, I don't know how much content your site has or how long it's been up for.
If you are having a few issues here and there, let us know what they are. We all have made rookie mistakes at some point in our webmaster careers. Maybe we can help you.
Hope this helps a little bit. In the end, if you absolutely don't want to keep your current site, I would recommend just flushing the whole thing.