Well, Since you've been running for a year,I'm assuming this is a version 1.2.x.
If your forum is working, you surely have a database of some sort. Open your config.php file, which is in your forum root, and look for the $db_type, which should be the first line. This is the database you are using, and you should see all your connecting information there.
The issue you have with the forum redirect is the same issue you have where you manually had to change a cache_config.php. The base url of the forum needs to be changed.
To do this, you need to go into your database. (depending on which database you have will determine how you can do this). you need to go into your config table and find the row o_base_url and change it to match your new url. You would then likely want to delete the files in your cache folder and you'll be all set.