You might need to restore a user's system configuration and working environment, either because of hardware failure or replacement, or because files have been damaged on the hard disk. You can use the Emergency Repair disk created during Windows NT installation to restore the system files. If you use the Emergency Repair disk to repair files such as the Registry hives, you will lose any changes that were made to the system after installation (unless you update your Emergency Repair disk using the REPAIR.EXE program from the Resource Kit disk).
You can use one of the following methods to reconstruct the system from backups, as described in "Backing Up and Restoring Registry Hives" in Chapter 11, "Registry Editor and Registry Administration":
If you are attempting to restore damaged SAM or Security hives, you must use this method. You cannot replace these hives while Windows NT is running. This means that if your system files are on an NTFS volume, you must have another instance of Windows NT available on that system to be able to restore the SAM and security hives. Or, you can use the Emergency Repair disk to restore the default SAM and Security hives (and subsequently lose any security changes made since Windows NT was installed).