Something may cause the error, look at the /etc/apache/ the configuration of apache server, this directory storage the apache parameters you have to include the .php extensions, the documents has a very good explain inside.

If you are trying to conect to another computer you can access using http://your-ip-adress/your-directory/file(.html or .php)

look the directory by default in some installations is /var/www

Include in your registration, your natural language, I can support you in Spanish

Bye

Frank