You will need
  • The computer with the OS installed,
  • boot disk
  • file Manager for DOS
There are several ways to repair the registry. The first and universal is that you need to backup files, either on removable media or on a hard drive partition where the operating system is not installed. It concerns the file SYSTEM.DAT, which is located in the system folder at %SystemRoot%\System32\Config.

To be sure, it is best to copy the entire folder with the system files before you begin to make changes. Thus, in the event of a failure, it will be enough just to copy this folder back to restore the registry.

If the loading of the operating system is impossible, use a boot disk, start with a simple file Manager and copy the folder into place.
If you don't want to copy all the data, then you can do export of the necessary parts of the registry to a reg file. To do this, click "start" in "Run" write regedit. Starts the standard program for editing the registry.

In the opened window select the required registry branch and click the right mouse button. In the popup menu, select "Export" and specify the place where you want to store the file.

After that, simply run this file and accept the suggested changes in the registry, in order to return to the original view.
In addition to the standard facilities provided by the operating system, there are many programs designed to edit the registry. In all of these programs provide the ability to back up the registry or parts of it. It is better to use such programs.