If you have recently changed or updated the cPanel or your server php version from php 5.6 to php 7.1 and your wordpress/wp-admin is not loading.
You need to fix the wp-login.php in the root folder of your website.
Login via FTP to your website open the file wp-login.php
Find the line
$user = wp_signon( '', $secure_cookie ); ~around line 806
Replace it with
$user = wp_signon( array(), $secure_cookie );