More information is needed on what you trying to do. But before you do anything I would recommend backing up files. (always a good practice)
If you have somehow corrupted your profile then you should log in as an administrator account and go to the control panel and then user accounts. There you can create a new profile. If you need to delete data associated with a profile then you need to right-click on My Computer, goto properties, advanced tab, then click settings in the user profiles section.
Between those two sections, you should be able to figure out how to make a new profile. As for "rebuilding" one, the only real way to do this is to delete the one you have now and then create one with the same name and then setup whatever you need.
Hope this helps.