Please help me!

Hi! My name is Nico. I live in Germany and I have a big problem with my PHP-Parser. I wanted to install the new version, Number 4.1.1.. And so I first deleted the old version from my Directory c:\program files\php. The new version was installed with the Install Shield for Windows to c:\php. And now the parser doesn't work any more. By opening a PHP-Script through http://localhost/script.php, I get a "500-Servererror". Executing the script is enabled in the Personal Web Server 4.0, that I use. What else can I do??? Please help me, if possible, write in german, to nico.haase@web.de !!! Thank you! Nico