It is likely that the problem resides outside of the script. If this is the first time you install any php script, chances are the website is not configured properly. You should install different scripts on your web site and see if similar problems persist. If so, ask your web administrator to take a look at your web site.
If you have already installed many different scripts and made it work successfully, then I suspect ".htaccess" file is preventing it from displaying web pages. It could be the .htaccess file in the root folder of your website. Also, if you installed the script inside of another script folder(such as a blog script ), the .htaccess of the outside script may have blocked the page access.
Although this is rare these days, wrong folder permissions may have caused the problem. Make sure the script folder has an executable permission.
In any case, the problem is likely outside of the script so tweaking the script files won't help you.