First check to see if http://www.yourwebsite.com/display.php is working.
Make sure the files are uploaded to the root '/' directory.
If the files are NOT located in the same and/or root folder, you will need to update ad_logic.php. At the top of ad_logic.php you should see the following:
$PATH_TO_AD_FILE = '_ad_file.csv';
Make sure you update _ad_file.csv to the correct location relative to ad_logic.php.