If you've been banned, starting a new account isn't allowed, unless it's for the purpose of appealing your ban in the Meta section.
It is the rule of the forum. But if anyone creates an account after being banned from the account still can create an account and until someone reports it is ban evasion and/or the admin/moderator/system can not detect the ban evasion there will have no problem using the account. But if anyone shows proof of the ban evasion then the admin/moderator can ban the newly created account.