application/x-httpd-php File download when open index.php

Hello, we have installed CWP, on the Server are 2 Domains running. One is a Wordpress, the second one old Webpage coded with php.
The Wordpress Page works fine, the other one when we open the Page we get asked to download the file:

application/x-httpd-php

Server :

Apache version: Apache/2.2.27
PHP version: 5.4.45 [PHP Switcher]
 Distro Name: CentOS release 6.8 (Final)
Kernel Version: 2.6.32-042stab120.11

Thanks for fast help.

We have tried several Solutions when you google the error, nothing has worked out so far.