Step 1: Enable Error Printing in PHP OR Enable DEVELOPER_MODE
In order to find out the bug, enable errors for your PHP.
If that doesn't work, edit php.ini (see http://php.net/manual/en/errorfunc.configuration.php) and set:
If you don't know where your php.ini is located use:
<?php phpinfo(); ?>
And locate "configuration file (php.ini) path".
Step 2: Debug your Apache / Web Server Log
If you still don't get any errors in PHP, the problem has to be with web server:
If you are using Apache, locate
error.log and see if they contain messages related to this issue.
tail -f xxx.log allows you to track changes in a log in real-time (very useful for debugging).
Step 3: Check directory and file permission
Directory permission must be 755 other permissions like (752, 753, 756, and 777) cause limitation and will not work..
File permission must be 644 other permissions like (642, 643, 646 and 647) cause limitation and will not work..