if you are testing paypal IPN in your local computer it will never work because paypal can’t access your local machine, it needs to be on a accessible server.
if you want to test if your server is receiving the paypal call try posting the txn_id variable ($_POST[‘txn_id’] ) to your home page, if you get a empty page your are good if you get and error or 404 page your site is not receiving the call.
I you get and error please let us know what it is.