Recovering the Windows XP registry if it won't boot

It is possible to make registry modifications which mean you can no longer boot into your installation of Windows XP.

Microsoft knowledgebase article 307545 describes one laborious way of recovering the situtation -- basically the idea is to use the recovery console to copy 'clean' (default) versions of the five registry hive files over the actual files, reboot, retrieve a backup of the same registry files from System Restore, boot back into recovery console and copy the recovered files in place.

A rather quicker and easier way is possible if you can use a boot disk or CD such as Knoppix to access the filesystem. You can then directly copy the five registry hive files from the system restore snapshot over the 'live' files. In particular, find the folder named something like C:\System Volume Information\_restore{D78358235-78....}\RP1\Snapshot and copy from it the files _REGISTRY_USER_.DEFAULT, _REGISTRY_MACHINE_SECURITY, _REGISTRY_MACHINE_SOFTWARE, _REGISTRY_MACHINE_SYSTEM, _REGISTRY_MACHINE_SAM. These five files should end up in C:\windows\system32\config, named DEFAULT, SECURITY, SOFTWARE, SYSTEM and SAM respectively.

Keep copies of the files you're overwriting, of course...