Sudden blank page on WordPress Admin Dashboard - php

Question

My WordPress Admin Dashboard is experiencing an issue which I have never encountered before. I have not made any updates/changes on WordPress and any plugins. Yet, suddenly my WordPress Admin Dashboard has become like the attached image below.
What I have tried so far to fix this issue:
(1) Increased the WP_MEMORY_LIMIT but it did not worked out
(2) Tried to change wp-admin\includes\screen.php on line 706:
from <?php echo self::$this->_help_sidebar; ?>
to <?php echo $this->_help_sidebar; ?>
But my screen.php file has less than 300 lines of code and does not contain <?php echo self::$this->_help_sidebar; ?> in it. So I cannot change it.
(3) Disabled all plugins(10) by renaming the "plugins" folder and it did solved the blank page issue.
(4) I have set WP_DEBUG to TRUE and got the following messages:
Undefined property: wpdb::$connect_errno in /local/www/html/xxxxx/wp-includes/wp-db.php on line 684 Notice: Undefined property: wpdb::$connect_errno in /local/www/html/xxxxx/wp-includes/wp-db.php on line 684 Notice: The called constructor method for WP_Widget in WPAC_Nav_Menu_Widget is deprecated since version 4.3.0! Use
__construct()
instead. in /local/www/html/xxxxx/wp-includes/functions.php on line 3764 Notice: The called constructor method for WP_Widget in Genesis_Featured_Post_with_title is deprecated since version 4.3.0! Use
__construct()
instead. in /local/www/html/xxxxx/wp-includes/functions.php on line 3764 Notice: Constant FORCE_SSL_ADMIN already defined in /local/www/html/xxxxx/wp-config.php 
(5) Disabled the plugins(10) one by one to find out which plugin was the culprit. Interesting enough is that whichever plugin I disabled the blank page issues was still solved . This made it difficult for me to isolate which plugin was the culprit. I might be totally wrong thinking that the plugins may be causing this blank page issues. Currently, I have no idea how to solve/approach this issue and why this is happening.
Any help would be appreciated very much!