Launching IE- porn site keeps showing up

I have a client that everytime he opens IE it defaults to a porn site. I have deleted all temp files, windows\downloaded program files, any links I could find and edited the registry. The site still appears upon IE launch. When the page opens it continually generates different porn pages and basically locks up the computer. It also removes Norton AV. I appreciate any and all help as I prefer not to do a complete rebuild.