OSCLASS：self :: $ instance = new self;

I have setup osclass in a directory of my website. When I try to access this directory(index.php), it returns blank page with response status 200. I don't see any error in the apache error log. I also have included these lines and no errors are reported.

error_reporting(E_ALL); 
ini_set('display_errors', 1);

When I tried to examine the php code, I found that the line self::$instance = new self; is not executed in this function:

    public static function newInstance()
    {
        if(!self::$instance instanceof self) {
            self::$instance = new self;  //It appears theres a problem with this line
        }
        return self::$instance;
    }

This is in class Rewrite. This functions is called from oc-load.php:

$instance is declared private static: private static $instance;

if( OC_ADMIN ) {
  ....
  ....
} else {
  // init Rewrite class only if it's the frontend   
  Rewrite::newInstance()->init();   
}

I am just beginning with oop php. I understand that the above line is trying to create a new instance of class Rewrite. But I'm not able to find why its not executed.

Can you please tell me why this fails?