Userlist Missing!!

The situation is this: Karthik's lab computer, with Windows XP installed, boots up normally. But when it reaches the Logon screen, it asks to click on any "listed" username... But to our great suprise, we see no users listed. We tried the double Ctrl+Alt+Del to login via the conventional, Windows 2000 style, "text-box" based logon screen... It kicked out Administrator as well as Karthik, two of the three users of the system.

Now, the regular troubleshooting sequence was tested... Restart... Safe Mode... Last Known Good Config... Naada! Nothing worked!! From the forum http://www.experts-exchange.com (Karthik paid 10 bucks for a 1 month membership!!!), the most important information I gained was abt the s/w Offline NT Password Registry Editor. http://home.eunet.no/~pnordahl/ntpasswd/. The software can be downloaded free of cost and can be burnt onto a CD which will be bootable. Once booted from the CD, it loads a linux kernal and asks a few questions, answering which one may alter tha password of any user of the system, including adminstrator. The gist of the s/w, I think, is that it knows how to decode the cryptic password information stored in the registry's SAM file (usually found in \winnt\system32\config and is a part of registry).

The site says abt SAM:

"NT stores it's user information including crypted versions of the passwords in a file called 'sam', usually found in \winnt\system32\config. This file is a part of the registry, in a binary format previously undocumented, and not easily accessible. But thanks to a German(?) named B.D, I've now made a program that understands the registry. As far as I know, Microsoft provides no way of changing the password if you cannot log in as someone with appropriate privileges, except restoring the registry files from the rescuefloppy. "

However, in his case, it didnt work, because it found no users in the registry. That means that the users part of his registry might have been corrupted.

The next arrow in my quiver was to repair-intstall XP on his comp! But that too gave up on me, because it just restored the system files without touching the registry.

Finally, unfortunately, we had to use the pick-axe method - To format C: and reinstall windows!

The reason for the failure of userlist is still unknown. For me, it looks like something needs to be done regarding his power-supply, because power from it made my laptop touchpad go crazy, and this is the second time within a month where his system had to be restored this way. (The first time, it was some "security service failure" error even before it reached the login screen, which, again, remains anonymous to me till date).