You need to find out how it keeps reloading itself. Search for it in the registry (run\regedit). It's usually something like local_user\software\microsoft\windows\run or runonce or runservices. Delete any references to it there.

There's also one called AppInit_DLLs which is the most evil thing Microsoft ever did to its own software. Just search for it in the registry and delete anything suspicious (there really shouldn't be anything there).

Now tell us: Did you see anything suspicious in these areas? Tell us what you did see even if you don't think it's suspicious. Remember, real men don't use antivirus software. Ever. Antivirus software = worse than crying.