Your threads title and content do not make that clear what you actually did. In any case you should never rename the root account as the system depends (partially configurable, partially hardcoded) on it. And if you feel compelled to mess with things at least try to understand what you're going to mess with before
you're doing it. Please fill in your distribution details in your User control panel
, boot your distributions installer CD (or a Live CD) in repair mode, get a shell and then restore things.