Well, some of that makes sense. 'localhost' is a special name and it always refers to the machine you are running from. So, if you use localhost in the URL on the linux box, it tries to connects to the web server on itself and works. If you use local host on the laptop it will try to connect to a web server on itself and fails.
Try
http://name of linux box/Sarah_new/index.php from the laptop and see if that works.