Try uninstalling all Norton products.
There may be a removal tool from Symantic to completely remove all traces.
or
search the registry if you dare and remove any links that appear to call on .dll or .exe files to run.
Run MSconfig and check that no Symantic/Norton links are running.
or
reformat and use AVG or Avast or AntiVir. I personally prefer AVG over Avast but I’ve heard that AntiVir is pretty good also.