Did you download and try all three of the programs which were suggested ?
Just to be clear, download and install and run, in this order Lavasoft AdAware Free (ChuckFicken's first suggestion), then Spybot Serach and Destroy (his second suggestion) and finally Malwarebytes anti-malware (which is the one I suggested). Links are in the responses to your first question.
There is at least one piece of malware (Vundo and variants) which hooks itself into the login process and uses random file names to make itself difficult to get rid of. If your mysterious program is not a virus, Norton may not spot it, but one or more of the suggested programs should get rid of it, that's why you should download install and and run all three, just to be on the safe side.