Win32/Sality.Nar Virus

Good day! I'm using a trial version of ESET Smart Security. From what I've heard from computer experts, ESET's NOD32 is one of the leading antivirus brands in the world. I'm very satisfied with the results after I've used it. But still there are some problems in my computer. It cannot totally remove Win32/Sality.NAR virus. The task manager is still disabled, some programs show errors when they are opened, and worst, my computer starts to get slower and slower. The antivirus detects this virus but when it comes to this file (C:\WINDOWS\system32\rundll32.exe), it always show: error while cleaning. And I think that's the reason why the virus keep on infecting files that has been cleaned.
I appreciate your assistance.
Thank you.

 

Of course, that's most likely because system files, that are already running, are infected. You should create a rescue cd, boot from it and clean your computer.