Symptoms -Windows Log on and Log off immediately
Cause – Virus has deleted userinit.exe from system32 folder
Solution – It can be resolved after successfully restoring the userinit.exe
If that machine is on LAN then it is very easy to solve that problem.
You will find a copy of that userinit.exe in that machine inside c:\windows\system32\dllcache
To copy that file, access from another machine by c$ and copy the file from dllcache location to c:\windows\system32 location.
that’s it !
Restart that machine and you will now able to log in through user name and password.
If that machine is standalone machine then boot the machine from a floppy disk and copy the userinit.exe from c:\windows\system32 and paste it inside c:\windows\system32 and check it now