If you edit something in the registry and Windows doesn’t start it might seem like you have a really big problem as you no longer can access and edit the registry to fix the problem. But if you have access to another hard drive with a working copy of Windows or another computer with Windows, you can plug in your “sick” hard drive and access its registry editor. Following are my directions for Windows 7. For Windows XP see here: http://forums.pcper.com/showthread.php?409638-Remote-Registry-Editing-and-Registry-Recovery
- Go into Registry Editor (run… regedit)
- Highlight HKEY_LOCAL_MACHINE
- Click File -> Load Hive
- Browse to A:WindowsSystem32config (replace A with whatever drive letter you have assigned to your sick hard drive).
- Find SYSTEM and open it.
- Now you will be asked to create a name for the hive. I enter “a” so it shows up first on the list.
- Qhen you are finished editing your registry remotely move to the top level of the named key (“a” in this case), and click File->Unload Hive. DO NOT SKIP THIS STEP
Now when you go into “a” you will see all the HKEY_LOCAL_MACHINE registry entries for your sick hard drive with the exception of SYSTEM/CurrentControlSet. This key cannot be accessed remotely. If that’s where the problem resides there is still one other way to get Windows on its feet again.
The SYSTEM file
If you had a system restore point saved on your sick drive, navigate to A:WindowsSystem32configRegBack (again replace A with the drive letter assigned to the sick drive) and copy the SYSTEM file. Paste it into A:WindowsSystem32config, replacing the file that is there currently. The only likely downside will be that you will have to re-install any programs since that restore point was created.
Once again, when finished remember to move to the top level of the named key (“a”), and click File->Unload Hive!
Alternatively, if you have a clone of the sick drive from before it was sick you can copy the SYSTEM file from A:WindowsSystem32config (replacing A with the drive letter assigned to the CLONED DRIVE) instead. If you have both restore points on the sick drive AND a clone of the drive before it became sick I would recommend you to choose whichever SYSTEM file was created most recently.
Edit 19/08/2013: As I’ve written in my post about browser testing in VirtualBox there is a last resort I can recommend to those who need to bring their Windows installation back from the dead and don’t have access to either an extra hard drive with a copy of Windows or a restore point: the SYSTEM file might also be copied from a Windows installation in VirtualBox, though copying it from a clone of your hard drive or one of its restore points is always preferrable since all programs installed after the file’s creation will need to be re-installed.