Make a file called 'test.php' with contents like so:
<?PHP
phpinfo();
?>
If you see some tables with version numbers, settings, and such, then PHP is working just fine.
EDIT: While possible, though very unlikely, your host may have changed the extension used for PHP files (like .phtml or something similar). The .php extension is standard, however, and I see no reason for them to change it, so just stick with .php for now. If that does not work, you might try giving us the name and/or website of your host.