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.

  1. Log in to cPanel or your DirectAdmin.
  3. In the left-hand pane, click the name of the Joomla database. A list of tables appears
  4. Click the _extensions table.
  5. In the name column, locate the plugin that you want to disable.
  6. 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.