I had successfully been running PHP and MySQL on my personal computer (Win XP). When I went to http://localhost, then a home page started up fine where I can click on a link on that page to run phpMyAdmin. (I used WAMP5 to download and install these files.)

Now when I go to http://localhost, a popup says that Firefox wants to know what program to use to open the PHP file. If I choose Firefox, then I see a page with the PHP code instead of the code execution. Yet all services, including the Apache server, are running.

I can't think of anything that would have invalidated PHP on my system. Any ideas?