Instead of the results of PHP-scripts in the browser, their content is displayed

The reason may be the presence of directives in the .htaccess file that try to override the PHP handler. An example of such a directive: SetHandler php56-cgi.

To fix the situation, you should check the contents of the .htaccess file for the presence of such directives. If there are any, you must either comment them out by adding the symbol # to the beginning of lines with them, or delete.