PWS vs. Apache

I might have a little (to use the term loosely) problem that I cannot seem to correct. In July, I stopped development work on a PHP/Apache/MySQL e-commerce project. Two days ago I attempted to run the application to determine what is left to complete. I started Apache and MySQL, started IE5, and entered http://localhost/index.php, hit enter and the response was "could not find the module"! I then entered http://localhost/ and the intro page to PWS loaded! Gads, what's going on? I did not change anything; matter of fact, I was never in a PHP/MySQL/Apache development mode since July. Can anyone lend some assistance? Bob