If you experienced a recently virus infection that may have been called “Virut” and are now experiencing a problem with logging in to your desktop, your antivirus or antispyware protection probably deleted the userinit.exe file.
There is no easy way to get this back without having some experience with troubleshooting computers.
The only advice I can give you is that you have to find a way to gain access to the file system to transfer a fresh copy of userinit.exe back into the C:\Windows folder.
If you have access to a boot disk like ERD Commander or Bart PE, those two will help.
If you have any questions, feel free to ask in the comments.