If you delete the %SystemRoot%\Repair folder in Windows NT 4.0, and don't have a backup, you won't be able to apply any new Service Pack, Repair your installation, or create an ERD.
The following procedure will recover a deleted Repair folder, if you are running Service Pack 3 or later:
1. Install an alternate copy of Windows NT, to a different Drive / Partition / Folder (in that order of preference).
2. Apply your latest Service Pack to this alternate install.
3. Boot the setup media and perform an update install of your primary installation.
4. Boot the alternate install (1st menu item) and copy the following from the alternate's System32 folder to the original System32 folder:
NOTE: If you are running SP4 or later, also copy:
5. Use Control Panel / System to set the default boot to your original installation (3rd menu item).
6. Shutdown and start your original install.
7. Apply / reapply your latest service pack.
NOTE: If you want to delete the alternate install, remove it's lines from c:\boot.ini and delete it's folder.