Windows XP computer logs on and instantly off

I had dell computer I had to fix. It turns out that the userinit.exe file was missing from the c:\windows\system32\ folder.

Of course, it was the last thing I checked. I removed all the win antispyware 2009 garbage files and checked the registy to make the winlogon key pointed to userinit.exe. I searched the hard drive for any copies of userinit.exe. I found 2. The most recent file came from the c:\windows\servicepackfiles\i386 folder. It looks like the customer tried to remove the spyware using anti spyware software and it ate the userinit.exe file. After I replaced the file, the computer logged in without any problems. I hope this helps someone else.