Windows XP Pro won’t log on

We recently had a virus which I believe Mbam found and removed, however now trying to logon we get a quick flash and then it instantly starts logging off. I tried something I read about going into recovery console and copy Userinit.exe to Wsaupdater.exe but that did not work. Any other ideas? Safe mode and any other way I try and get in brings me to the logon screen, which then after I enter the correct username and password starts the logging off message.