Sometimes it happens with bbPress and you won't be able to see the related admin menus because of some role permissions.
If you are logged in as admin and you no longer see the Forums menu in you WP-admin panel then you need to follow these steps to get them back:
- Install a plugin like Enhanced Capability Manager
- Edit the Admin/Super-admin role and make sure you have capabilities to manage forums/topics
- You can also try to reset the capabilities to their default.
- That should be it.