If you can't login you should use the tools.php file to reset the admin account....
Find the tools.php script in the do_not_upload folder of your vBulletin package and upload it to your admincp directory.
Then execute it from your browser, i.e. :
www.yourdomain.com/forum/admincp/tools.php and select the appropriate option
To reset the failed login execute
from phpmyadmin