Browsers without internet connectivity will highlight a known issue with OpsCenter where it tries to check latest versions from opscenter.datastax.com
When trying to connect to OpsCenter in a browser that does not have internet connectivity, existing clusters are not shown, instead the user is presented with the setup page to add a new cluster or manage an existing one even though there is an existing cluster configured
The opscenterd process tries to connect to http://opscenter.datastax.com/latest-version if it cannot then it presents the user with the choice as above. The following issue outlines this: https://datastax.jira.com/browse/OPSC-3285
Use a browser that has internet access if possible
This issue is fixed in OpsCenter Release 5.0.1 and greater
This problem is documented in the private Datastax jira, OPSC-3285.