Windows XP Login-Logoff Loop
Enter the Recovery Console
Boot the system using the Windows XP CD-ROM. In the first screen when the Setup begins, read the instructions press "R" (in the first screen) enter the Recovery Console. Type-in the built-in Administrator password to enter the Console. You'll see the prompt reading C:\Windows (Or any other drive-letter where you've installed XP)
Type the following command and press Enter.
COPY USERINIT.EXE WSAUPDATER.EXE
Quit Recovery Console by typing EXIT and restart Windows.
You'll be able to login successfully as you've created the wsaupdater.exe file (now, a copy of userinit.exe)
Now, change the USERINIT value in the registry and change it accordingly.
Click Start, Run and type REGEDIT. Navigate to:
HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ WindowsNT \ CurrentVersion \ Winlogon
In the right-pane, change the value of Userinit to "C:\WINDOWS\system32\userinit.exe,"
Type the above value exactly as given, including the comma - exclude the quotes.
Close Registry Editor and restart Windows. The Quick Launch settings should be retained now.