OS X Fails to boot !!


Hi, when I boot up Mac OS X, the "starting-up-progressebar" is not there, and the system fails to load. The mouse and everything works, but I can´t get into the system. Just see a blue background. I can hear the machine think sometimes, but never get´s into the system. I can get into 9.1, by holding the alt button down during a restart, and I took the "Disk First Aid" for a run, but nothing helps.. Would it help to re-install OS X again, I´ve got it on a seperate partition. And the files I´ve got for OS X now, won´t go away, will they ? Just install over, so my prefs and all are still there. Ain´t that possible ?
I´ve found out WHY it fails to boot. I´ve set my username to be the main owner of the main HD. It should be root, but now It´s my username. I got it to be my username by using an app called "get info", from Versiontracker.. How can I get it to be root again ? Some way to do it thru the command line ? Restart in the command thing, I mean... Please help :)