Question : All profiles are deleted, cannot log into Windows

I have a PC I'm working on who has a.... "unique" problem. It would appear that all the user profiles including the Administrator and Guest have disappeared. This is preventing all ability to log into the computer.  At first I thought for sure this was an obvious problem, the profiles have simply been removed from the welcome screen.  Since this is a Windows XP Home computer, normal access to the Administrator profile is restricted, but not through Safe Mode. However Safe Mode I would come to find was held under the same scrutiny as the normal welcome screen.

So by now I'm sure you have an idea of the next logical step! (I'm right there with you) I used a linux-based SAM editor that I mainly use to reset the administrator or other profile passwords when they have been forgotten or hacked. The venom of the problem is about to sink in...

Once booted, and where it needs to be to reset the passwords there were no profiles listed. A query of all users in registry was requested, and for the first time in my time as a tech, I found not a single user was in the registry, no Guest, no Admin, no users, no QBDataUser, Remote User, not even Beck performing "Loser", I mean nothing! The sign in front of me says "you are here", and so we are. I've scoured the net looking for similar issues... none so far.

I know I can pull the drive, port the data, and re-install Windows, but I sense through The Force that there may yet be a path to the light here in our darkest hour...

...Help me Obi-Wan Kenobi... you're my only hope...

Answer : All profiles are deleted, cannot log into Windows

Use any boot cd to get to either the recovery console or at a minimum to a command prompt. Once in, try executing this:

copy c:\windows\repair\sam c:\windows\system32\config\sam

If you are asked if you want to replace the existing file, say yes obviously. If there is a permission issue with the copy, you could execute the attrib command, like so:

attrib -h c:\windowes\system32\config\sam  (removes hidden)
attrib -s c:\windowes\system32\config\sam  (removes system
attrib -r c:\windowes\system32\config\sam  (removes read only)

this will replace the existing sam registry hive with the original install hive. This should allow you to login. Understand that there will be no users other than possible admin (with no password). If login is successful, you can then use system restore to go back in time and restore a previous registry and perhaps stop you from having to spend "30 days in the hole."