Editing a windows XP installation's registry without being able to log in

Solution 1:

You should be able to load the registry hive from your BartPE boot CD. You can follow the instructions listed here:

To load a hive into the registry

1. Open Registry Editor
2. In the registry tree (on the left), click either the HKEY_USERS or HKEY_LOCAL_MACHINE keys
3. On the File menu, click Load Hive.
4. In Look in, click the drive, folder, or network computer and folder that contains the hive you want to load.
5. Click Open.
6. In Key Name, type the name that you want to assign to the hive, and then click OK.

Caution

• Incorrectly editing the registry may severely damage your system. Before making changes to the registry, you should back up any valued data on your computer.

Solution 2:

You can edit your Windows XP Registry with Offline NT Password & Registry Editor which can be found here

Remember to backup your registry files.