Simple PHP Include Question

I have a really simple site that has been working for several years. It has a main index page and depending on the variable it is called with, displays different content in that page. I know literally nothing about PHP and someone else gave me the code forever ago. All the sudden the code stopped working. I have no clue why.

http://www.mysite.com/?con=about

“con” is the variable and “about” is another is the page I want displayed which should include a file named about.php.

If the page is called with an invalid variable or with none, it should revert to main.php.

The php code is:

   	<?
		$ext = ".php";
		$id = $_GET['con'].$ext;
		if (file_exists($id))
		{
		include($id);
		} else {
		include("main.php");
		}
	?>

The files are all there, if I change the addresses to:

http://www.mysite.com/about.php

I think there must be something stupidly simple, but don’t know where to start… except for to ask on this forum.

Interestingly enough, I copied the code to another website that is not hosted on GoDaddy, and it works. There must be something in that code that has recently been blocked on a GoDaddy cpanel host.