Windows log off automatically

Problem: During log in, it logs off immediately

Userinit is missing from the registry.

With the help of ERD commander or BartPE, in registry:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Winlogon

enter new value:

Userinit

double click on it and enter:

C:\WINDOWS\system32\userinit.exe,

(comma is part of it)

UPDATE;
copy userinit from Windows XP cd, i386/windows/userinit.exe_
This allows boot in safe mode and cleaning , there was virus Trojan.Agent.