can you be more specific?
Usually, clans will kick members for joining other clans, and clans will not let someone in who is already in a clan.
The action of leaving one clan and joining another is known as Clan hopping, and is highly frowned apon.
If a clans forum is closed, do you mean taht the clan does not et have a forum, and is unofficial, or it was official, and then died because of inactivity?