How To Recover System To Factory Settings

Recently I was attacked with malware and I had no internet security. It messed up some programs, changed the description of processes etc. I read up on how to get rid of malware and such, and I got Malwarebytes, SpyBot - search&destroy, and finally Avast! computer antivirus. After running scans with malwarebytes and Spybot, removing all the trojans and programs that were affected, I used ccleaner to clean the registry. Although I did all that, it seems like there is still something in my computer because spybot keeps scanning the same files over and over, and both Malwarebytes and Avast! keep saying that a malware threat had been stopped, while showing a URL that I never even connected to. Sometimes it even happends when internet explorer is off. what I really want to do is to restore my PC to the factory settings and start with a fresh NEW system. I'll make sure to get AVAST right away to insure security. As for backing up files, I'm afraid that the virus would somehow be in certain files and infect my computer again. Nothing really important that I'd lose. So I don't really mind so much to do a full factory reset.