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Boot of the Offline NT Password and Registry Editor cd and unlock and clear the administrator password. Write files back to the filesystem when asked to.
mount.ntfs-3g /dev/sda1 /mnt
cd /mnt/Windows/system32/config chntpw SAM system SECURITY
This will run chntpw for administrator. Unlock the account if necessary and/or clear the password. Answer yes to writing hives to the filesystem.