Adware problem

My computer is driving me nuts cause i get a popup every 20 minutes saying I have malicious programs and that i need to go to regfix.com to download a repair. This is obviously an advertising scheme, but i can't get rid of it. I've tried ad aware, spybot, AVG antivirus, and hijackthis!, but it wont go away. I did all of these while in safe mode with my system restore off. Any Help?