Login Logoff looping while starting windows XP

http://support.microsoft.com/kb/555648


Edit these values and type the correct path of shell : Shell = explorer.exe Userinit=X:\windows\system32\userinit.exe NOTE: These files may also be deleted by spywares. You may need to extract them using Windows CD. Steps for rectifying this problem:
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Log on to a networked computer.
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Run Regedit.exe
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Point your cursor to HKEY_LOCAL_MACHINE
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Select File > Connect Remote Registry
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Type computer name (infected computer)
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Navigate to the following location in registry of destination or infected computer HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
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Edit these two values in right pane: Shell Userinit
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Change these two values to Shell=explorer.exe Userinit = x:\windows\system32\userinit.exe
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Exit from Registry
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Restart Infected computer.
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You should be able to log on to computer.