simple php problem

I am a php newbie, and am having trouble running the install.php. My server is a plesk style host, and the php option is ‘CGI Application’, though I have also tried with it set to ‘Apache module’. When I ftp://www.smaltiaustralia.com/httpdocs/wpexample/wp-admin/install.php in my Chrome browser, it displays the script, as expected. However when I try to run the script by entering the URL https://www.smaltiaustralia.com/httpdocs/wpexample/wp-admin/install.php, it gives me a ‘404 not found’.
What am I doing wrong?
Thanks in advance
David