I, too, have an issue with an XP Login/Logout loop. To work to solve the hard drive was installed into another computer as a slave and ran a virus detection program. A virus was found, but don't remember the name. The virus was removed. After reinstalling the HD as the primary drive on the original computer, the loop still happens without change and also loops in booting Safe Mode.
The hard drive was then put back into the other computer as a slave. Then copied wsaupdater.exe to userinit.exe in the system32 folder. Then put the hard drive back as primary in the original computer, but the login/logout loop still occurs without change during normal and safe mode boots.
Many solutions for this prooblem describe that a registry key: HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ WindowsNT \ CurrentVersion \ Winlogon
needs to be changed to "C:\WINDOWS\system32\userinit.exe" using REGEDIT. Because of the login loop, I cannot conceive how to execute REGEDIT. Doing a Windows Recovery is not possible because there is no recovery partition and the original Windows XP installation CD's are not available. Is there a way to execute REGEDIT on the machine when I cannot login to it? Is REGEDIT accessable from the Command Prompt? Can REGEDIT be used to edit the registry on a slave drive instead of the primary drive (which looks like the easiest way to change the registry entry)?
Here's what I'm seeing:
1. During boot, everything goes normal until the Welcome login screen.
2. When I click on the account name, the system reports that it is loading personal settings.
3. The Desktop wallpaper shows for a few seconds without also showing any other icons or a Start button.
4. The Welcome login screen shows again and reports that it is logging off.
5. The Welcome login screen shows the user account icons and is ready for someone to login again.