You could try and manually insert an account via the mysql prompt.
The only problem is that the account would be incomplete, but you could try it .. it might get you in.
Then you could create a good and proper account within the forum itself and make it an administrator.
There's a problem with that. The passwords are encrypted into the database and hard to crack... I've personally seen it and I can't figure it out.
The only way I can suggest is to reinstall the forum... It's the only thing I can help though as actually creating an account via phpMyAdmin is difficult if you know how it's encrypted..