There are several reasons why you can get locked out of the WordPress admin or wp-admin screen. The first is an incorrect password error. No matter the reason for this you can reset it manually by accessing wp-config.php file and editing the main admin user account password. You may also be locked out if account lost admin privileges. In this case you access wp_users section of your database and create new admin account in several steps. Lock out may also be due to a security plugin problem. If a security plugin is suspected, deactivate it and test if you can get access. Another reason for lock out could be an error establishing a database connection for which there is a tutorial by Freddy Muriuki. Finally you may experience a white screen of death caused by faulty plugins, faulty theme or a syntax error in one of your files.
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How to Fix the Locked Out of wp-admin Issue