Try creating a file called test.php with the following as its contents
PHP Formatted Code
then access this page in your browser... if you do not see the page output a table with all of your PHP configuration, the browser shwos the above code, or there are errors then you have an issue with your PHP install
if NOTHING shows up then you have a problem with Apache probally...
you have not said what platform or versions you are running so this is just general troubleshooting suggestions