WinXP Pro SP2 logon loggoff error

Hey all, ive google'd for answers on this problem but found the same thing over and over. I did what was suggested but still no success, so hopefully someone here has had same problem or heard of it before and solved it.

I have a pc that when i start up it reaches the user profile window. You put in your user name and password or administrator and password and click ok. It starts to log into windows and then immediately loggs off, save settings and returns to the user profile login window. And that is it.

Aparatnly it is caused by one of three virusses. Ive taken the hardrive out placed in another pc and scaned the drive with AVG, Norton and Adaware 6 antivirus programs. All been updated to latest virus defenitions. No virus was detected.

NOW please READ FOLLOWING CAREFULLY!
Before someone here say i must go Start, regedit etc.. I CANNOT ENTER WINDOWS in any form whatsoever. Not safe mode, safe mode command prompt, Use last know working..., nothing lets me enter windows. I am stressing this cause on other forums this was suggested after the user said they cant enter windows.

Apparatnly i need to replace the c;\windows\system32\userinit.exe file and update the registry entry in HKEY_Local\etc.... and fix the shell line and userinit key. I did so but no luck.

ALSO reformating is not an option, the user does not have all his application cd's and so on. SO it is really the very very last resort.

Basically i am hoping someone here has a idea! Thx in advance

I always use an External USB HD enclosure for things like that. They cost under $40 and you'll use it many times.

You mount the drive in the enclosure, connect it to another PC and boot it. Windows will give it a drive letter. It acts like any external drive. Delete whatever you want and put it back in the original PC.

First off have you tried safe mode? If not try it if so and it failed then you need to use the Recovery Console.
For it to work you will need their Administrator password if any and a Windows XP disk.
Look at this page for instructions on how to start the recovery console and how to use it: http://support.microsoft.com/KB/314058
It just uses standard DOS commands so if you are already familiar with DOS you won't have any trouble with it.