Should you have a module installed that locks you out of your back office (for instance the IP block module), you can disable this in the Joomla database.
This article tells you how.
- Log in to cPanel or your DirectAdmin.
- In the Databases section of the cPanel home screen, click phpMyAdmin.
- In the left-hand pane, click the name of the Joomla database. A list of tables appears
- Click the _extensions table.
- In the name column, locate the plugin that you want to disable.
- In the same row, double-click the value in the enabled column.
Now your extension is disabled and you can log in again, to fix the issue.