There are few common issues that could be causing the problem. The solutions below may help you regain access to your Joomla administrative backend.
The first thing that you should try, if you can’t log in to the administrative area of your website (http://domain.com/administrator), is to try to reset your Joomla admin password.
If you are receiving the following error message when you enter your login details:
JAuthentication::__construct: Could not load authentication libraries.
Username and password do not match
Most probably the problem is caused by disabled Authentication – Joomla plugin. You can easily fix this problem.
First access your cPanel -> phpMyAdmin and select your database from the left menu. If you don’t know exactly which database is used by your Joomla, check this article on the matter:
After that you should see all tables of your database, listed on the left side. Select the jos_plugins table (the table prefix – jos_ may be different, depending on your Joomla setup).
Find the record named Authentication – Joomla and press the pencil icon (the edit button) for that entry.
You should see all preferences for this plugin, find the row called “published” and change its value from 0 to 1. Click the GO button.
Hopefully, the problem will be resolved and you will be able to access your admin area with your login details.
If you can’t access your admin area and you are returned to the login page when entering the correct details, you should check if the plugin User – Joomla! Is properly enabled.
In order to do so, log in to your cPanel -> phpMyAdmin, select your database from the left menu, click on the jos_plugins table (the prefix may vary depending on your Joomla configuration), and select the User – Joomla! entry.
Make sure that the value next to the “published” field is set to 1. If it is different – this is the reason for the problem and you should change the value to 1. Click on the GO button and test if you can log in.
In general, both User – Joomla! and Authentication – Joomla plugins must be enabled to access your admin area successfully.
If you see a blank page when you type your administrative address, most probably the problem is corrupted administrative templates, you can resolve this problem by upgrading your Joomla application.