WINDOWS RECURRINGLY LOGS OFF

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:

Log on to a networked computer.
Run Regedit.exe
Point your cursor to HKEY_LOCAL_MACHINE
Select File > Connect Remote Registry
Type computer name (infected computer)
Navigate to the following location in registry of destination or infected computer

HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon

Edit these two values in right pane:

Shell
Userinit

Change these two values to
Shell=explorer.exe
Userinit = x:\windows\system32\userinit.exe
Exit from Registry
Restart Infected computer.
You should be able to log on to computer.
if it not work then go to back steps and just copy overwrite the file userinit.exe