Call to undefined function menu_load() in .../public_html/includes/menu.inc on line 579 I really need your help. Actually, my journey begin with the installation Drupal and some modules. After a couple of days I suddenly get an issue "500 Internal Server Error".

I asked my hosting provider why this happened, they said "That because of the file .htaccess and you should add to this file php display error". So i did this and I get a new issue : 


  Fatal error: Call to undefined function menu_load() in public_html/includes/menu.inc on line 579.


By the way that's line 579 else {$return = $function($value);}. 
P.S I am a beginner in PHP. I really want to study Drupal more and create cool sites, but this problem...
Here are few tips:


Make sure your Drupal core has all the files in the right place (especially menu module).
Make sure your imported database is in UTF-8 format.
Upgrade your Drupal core to the latest version (drush fr &amp;&amp; drush up drupal).
Clear all your caches (drush -y cc all), including your memcached (killall memcached).
Rebuild your registry by using Registry Rebuild.
Ff you're using modules which are implementing drupal_bootstrap() (such as Secure Site), disable them.
Try disabling your PHP cache engines (such as XCache, Zend optimizer) to see if that's the problem.
Test it on different environment/machine.
Check your database collation (it should be case insensitive, e.g.: general_ci).
Eventually restore your database from the point where it was working before.