It seems that the Apache Handlers for .php files are not set correctly. Did you try accessing other php files (let's say, even a dummy phpinfo.php file) and see if it executes instead of downloading?

:'(

When I try other files, they are the same, they all want to open - save - cancel.

Kind regards
The bhoy

It's your sever's apache handler. If you have CPanel, try checking the "Apache Handlers" area and make sure that ".php" is set to "application/x-httpd-php" If no, play around with .htaccess by adding someting like this:

AddHandler application/x-httpd-php .php