Macbook doesn't boot after file sharing preference screw-up..

[VinylDutch]

While trying to get file sharing between other macs working I made the mistake of removing the administrator account from the boot HD in the file sharing preference panel. I believe that this is the cause as a couple of Min after that my mac grinded to a hold, and I rebooted, everything boots normally but my macbook doesn't continues past the blue screen before that the os is completely loaded...
I tried to repair the damage by putting the HD in an external enclosure but couldn't find a way in OSX to fix the problem on a external HD.
Please Help,
Thanks!