I can't remove "Positive Finds" adware from my PC. Please Help!

Hello, I've managed to infect my PC with some annoying adware which pops up adverts all over my browsers.  I have Norton AntiVirus running on my Windows 7 laptop and have so far tried scans with Norton Power Eraser, Malwarebytes Ani Malware and SUPERAntispyware which detect adware and remove it but "Positive Finds" keeps coming back whenever I run a browser.  Any help would be gratefully appreciated!