In some cases, you may need to edit the registry of a system, but are unable to access the regedit tool from the system in question. This may be because a blue screen, virus infection, or similar problem won't let you get as far as a Run... prompt, or perhaps even a full Windows boot.

It is useful in these situations to boot to a Windows PE disc, which allows you to access a bootable Windows environment, usually from a CD. This environment will load a RAM drive as its primary disk storage, and allows you to access a number of useful troubleshooting tools.

One of these is the regedit tool, which is used to make changes to the registry. However, by default, this tool will load the registry of the PE environment, and not that of the system you are trying to fix. To edit the registry of the system in question, take the following steps.

1) Boot to a PE environment.
2) From the Start --> Run... prompt, type "regedit" and click the OK button.
3) Once the regedit screen has appeared, highlight the key that says HKEY_USERS.
4) From the File menu, select the "Load Hive" option. You will be prompted to select the appropriate Hive file that you wish to edit.
5) Navigate to [system hard drive]:\Windows\System32\Config, and select the file which corresponds to the registry Hive you wish to edit.

6) You will be asked to give a name for this branch. This won't really matter, but make it something that will make it easy for you to identify; perhaps "Joe's Hive" or "MyHKLMSAM"
7) This should allow you to now edit the registry residing on the hard drive in your machine.
8) Once you have made changes, highlight the Hive you loaded in steps 4-6, then click File --> Unload Hive.
9) You can now reboot your machine.