DCads

I am having some trouble removing a adware I have gotten from a limewire file. I have Norton anti-virus, Adware away and spybot search and destroy. I keep getting pop-ups that say ads served by dcads and occasionaly superior ads. I also get the occasional white flashing box in the upper left hand corner of my screen it's about 1 inch square and it's hardly there long enough for me to see it, it kind of flashes there and then its gone. I also keep getting some spybot notifications that something is trying to be changed in the registry I think. It's always the same one followed by the another one. I have been denying it every time.

I am getting desperate and am not a computer genius so please make this really simple (No abbreviations please and give me a step by step guide on how to do stuff)

Thanks in advance

-Tommy