Infinite XP Pro logon-logoff loop; usual fix doesn'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 (see: http://www.techrepublic.com/forums/discussions/windows-xp-logs-on-then-logs-back-off), but the offered "solution" does not work for me, even though I have edited the correct system registry to change the "userinit" key to either "...system32\userinit.exe" or "C:\Windows\Explorer.exe" (as others have suggested).

Also, all the drive letters in the registry correctly point to drive C (a problem many disk cloners have faced, but I know how to correct). Finally, whenever I try a repair install, I always get the DEFINITELY mistaken error message "Windows cannot find any disks").

I need an expert to point me to a working solution (unlike all the others). Thanks!