I wasted hours of searching Google back and forth, and found no solution: CiviCRM is set up as an internal only CRM system for an organisation (i.e. IP address 192.168.178.36) - so far, so good. Now I took the server with me to work on CiviCRM, so I changed the IP address to 192.168.2.36 accordingly.
I've changed Apaches httpd.conf, and Apache runs without issues. Drupal seems to come up fine, but whenever I want to access CiviCRM via http://192.168.2.36/q=civicrm/dashboard the website answers with
a) the former IP address (192.168.178.36) in the header of the result page,
b) "Access denied - you are not authorized to access this page."
I deleted the content of all drupal cache tables, I deleted the content of the "templates_c" directory - no success :-(
Please, can someone point me into the right direction?