NTUSER.DAT is the "Current User" part of the registry, deleting it will blow away your settings, and windows will make a new, default one. At least it's not a fatal error. Unlike some noob at work, he thought he would do a cleanup of his laptop's C drive, and deleted "ntldr" which is in the root. Unknown to him, that file is required when booting! No surprise to receive a panicky phone call at the helpdesk!