Ntfs.sys file is missing from the drivers folder under system32

I am using Windows XP as my OS, and it is attacked by a virus and the result was only a green screen appears.
I have executed ‘Spybot’ more than two times and it had deleted lots of files.
But, I am not able to connect the internet and there is no way to get updates. I have to reboot the system in safe mode, but it is not allowed to scan the computer.
Also, it gives an error message which says that ‘ntfs.sys file is missing from the ‘drivers’ folder under ‘system32’.
I have run the Windows Repair by using the installation CD.
I have copied ntfs.sys file from another system. But, both actions could not able to solve the problem.
Please help me to solve this problem.
Thanks in advance.
