Windows XP could not start because the following file is missing or corrupt

You may receive one of the following error messages and Windows XP won’t boot.

Windows XP could not start because the following file is missing or corrupt: \WINDOWS\SYSTEM32\CONFIG\SYSTEM

Windows XP could not start because the following file is missing or corrupt: \WINDOWS\SYSTEM32\CONFIG\SOFTWARE

Stop: c0000218 {Registry File Failure} The registry cannot load the hive (file): \SystemRoot\System32\Config\SOFTWARE or its log or alternate

System error: Lsass.exe
When trying to update a password the return status indicates that the value provided as the current password is not correct.

Microsoft has an article on how to recover from this:

How to recover from a corrupted registry that prevents windows XP from starting
http://support.microsoft.com/kb/307545

However, there’s a MUCH easier way.

Pull the hard drive from the system that’s not booting and add it as a slave drive into another system that works.
Fire up the working system.
Make sure you are viewing Hidden and System files (Tools -> Folder Options -> View).
Navigate to x:\System Volume Information (on the slave hard drive).  If you get an “Access Denied” error, right-click on the folder, go to Properties, Security, and then add Everyone to the list with at least Read rights.
If you don’t get the Security tab, you need to turn off Simple File Sharing (Tools -> Folder Options -> View).
Once you’re in, go to the _restore{bunchofnumbersandletters} folder.
In that folder, you will see a bunch of folders with an RP prefix.
These are the restore point folders on the system.
Check the dates and open the latest one (such as RP1153, or whatever).
Open the snapshot folder.

Copy the following files to C:\windows\system32\config:
_REGISTRY_MACHINE_SAM
_REGISTRY_MACHINE_SECURITY
_REGISTRY_MACHINE_SOFTWARE
_REGISTRY_MACHINE_SYSTEM

You can now close the snapshot folder.

Go to c:\windows\system32\config
Create a subfolder called backup
Move the following files to the backup folder you just created:
SAM, SECURITY, SOFTWARE, SYSTEM

Rename _REGISTRY_MACHINE_SAM to SAM
Rename _REGISTRY_MACHINE_SECURITY to SECURITY
Rename _REGISTRY_MACHINE_SOFTWARE to SOFTWARE
Rename _REGISTRY_MACHINE_SYSTEM to SOFTWARE

That’s it.  Shut the system down, put the hard drive back into the other system, and it should boot.  If it doesn’t, try another restore point.