Initialization Error when going to Civi CRM dashboard and adding pages/posts
It looks like CiviCRM is unable to access the CiviCRM database.  This is often separate from the content management system database (i.e. the database for WordPress, Drupal or Joomla).  This means that you may be able to access and log in to your website, but not access CiviCRM.

I'm not sure why this has happened in your case but I would suggest that you check your hosting package and see if there have been any changes to the databases or database users.  You should also check that the database settings in your CiviCRM settings file are correct.