I have the anti-virus protection service provided by Yahoo. It found 3 files infected by the virus when I ran it to scan my computer. However, it does not give me the option to kill the virus or delete the files. The files/viruses are still in my computer. How do I delete the infected files? Do I need to get another (real?) virus protection software or should the Yahoo version be sufficient? Thanks so much!

I recently was experiencing a lot of pop-ups so I decided to download a different virus protection called "avast". But stupid me, I forgot to uninstall my old virus protection software(Norton) and now my computer automatically turned off the virus protection. I'm not sure what to do? Is there a way to turn it back on? Do I have to uninstall 'avast'?
If I need to uninstall norton, how do i do it?