Block not showing on page
Likely a different module is being used to control block display: Context or Panels would be the most likely options.  It's possible someone wrote a custom module to disable blocks in the standard blocks interface to force you away from it.

Note: Drupal 6 is no longer officially supported by the community. While there are some places that are offering long term support for Drupal 6, you should plan to move to Drupal 7 or 8 soon.