Was the admin's default password of "changeme" ever changed? If you can not figure out the password, then
Now you have the default credentials (admin/changeme) back.
However, if you want to achieve similar results to clean all, then:
How are you trying to login? What credentials are you using?
When you say 'log in' you are trying to connect to it through the GUI? It doesn't support that. You can access it via the CLI and there is a rich thread on the commands at http://docs.splunk.com/Documentation/Splunk/latest/Admin/CLIadmincommands (thanks Drainy 😉
I am trying to login through the CLI. The Splunk Clean All is a CLI command.