I did remove the Active Directory plugin from the zope management at zport/manage and then I was able to see the users again. I probably should have mentioned that I was using that Active Directory connecto too. I saw some groups in there with funny names so I deleted them.
I resetup the Active Directory plugin and now I can see my users again. I guess it had nothing to do with my renaming the server... Sorry for the wild goose chase guys and thanks for your help!