in all of the php files I want to access with AJAX.
determines who can access the script and
determines what they can do.
The first two lines are for error reporting so you should see if the script crashes.
Now, that being fixed.
If you are still running http and not https that's likely the issue.
Chrome in particular will block access from a secure site to an insecure one. You'll notice this because a little shield icon will appear in the top right of Chrome. When you hover over it, it will tell you that the site is trying to run insecure scripts and it blocked it. You can click on that shield and unblock the site but you have to do it each and every time.
Finally, I recall reading somewhere recently that AJAX blocked requests to non-https sites. If you haven't gotten your certificate yet, now is a good time.
If you need a secure website, I personally use interserver.net. $5.00 a month and that includes a free cert.
That's my guess.