XP Pro logon-logoff loop; usual fixes don't work

What's happening is that one of my XP Pro/SP3 (32-bit) boxes is experiencing a commonly-reported problem wherein the XP boot process runs successfully but then goes into an infinite login/logoff loop (NOT a reboot loop). What happens is that the small Windows XP logo box comes up, says "Loading your personal settings", then it changes the text at the bottom to read "Logging off", whereupon the whole loop starts over again! (Note that I do not have a password).

There are a great many other identical tech support requests out there, including several here on this board (such as: http://forums.majorgeeks.com/showthread.php?t=209085, http://forums.majorgeeks.com/showthread.php?t=187458, http://forums.majorgeeks.com/showthread.php?t=118690, etc), but NONE of the suggested solutions in there or by Microsoft or by anything else I can find actually fixes my problem.

(1): There is no malware on the system (confirmed with several tools);

(2): The suggested Microsoft Answers solution involving userinit.exe and the userinit HKLM registry key (see the post by pjn33 at: http://answers.microsoft.com/en-us/...-in-loop/fa39a531-b865-4de5-a0fd-2ddc075aacff ), doesn't work for me (i.e., no change)

(3): A variation of (2) above is to change the userinit key to point to C:\Windows\Explorer.exe", also doesn't work.

(4): There's no evidence of a corrupted registry (that system worked perfectly until this suddenly started happening).

(5): This logon/logoff loop is reported to occur after cloning a system disk to another drive or partition, which results in the system registry pointing to a drive letter other than "C". I did face that problem earlier, but I know how to fix that and the fix worked perfectly (Terabyte OS Deployment tool (from the company that makes BootIt Bare Metal) has a mind-bogglingly great script that performs that task thoroughly and correctly. I've confirmed that the registry entries all point to drive "C", so that's not the problem either.

(6): I'd happily try a Repair Install, but every time I try I get the same obviously wrong message to the effect that "Windows cannot find any disk drives in this system". And none of the proposed solutions to that problem work either (the only disk is the system disk, which is a two-disk RAID 0 array running off an Adaptec SCSI-320 adapter).

(7): When I try to boot using "Last known good configuration" or "Safe Mode", the exact same logon/logoff loop occurs anyway.

(8): The suggestion to use SFC is highly problematic for me; it's never worked as expected and described for me (It has to do with an installation setting, which I deliberately disabled).

(9): To do most of the above work, I boot into "Mini XP" mode on Hirens Boot CD v15.2, which has allowed me to run DSKCHK and many, many other tools that confirm that not only does my SCSI-320 system disk array work perfectly, but none of the tools can find anything wrong whatsoever.


So, what I need is an expert to point me towrds a working solution (unlike all the others). I'm a highly knowledgeable user, but I'm completely stuck!

Please help!