Try this method:
https://vborg.vbsupport.ru/showthread.php?t=259619
If doing that does not work, while in phpmyadmin check your administrator accounts, in the user table, alternatively you can run this query in phpmyadmin (include db prefix if one is used):
Code:
SELECT * FROM `user` WHERE userid = 6;
Run the query, make sure the admins listed are indeed proper admins if not then something suspect is going on.
You can see the vb_ prefix before the tables and also in config.php
PHP Code:
// ****** TABLE PREFIX ******
// Prefix that your vBulletin tables have in the database.
$config['Database']['tableprefix'] = 'vb_';