I need a free site where I can download a anti-virus protection program.. but it needs to be free.

You can try Avira. Avira AntiVir Personal - Free Antivirus (http://www.avira.com/en/avira-free-antivirus)
Click on the download button on the left. Don't click on the trial one.

If you don't like avira you can try Avast, or AVG.

Don't have two antivirus programs installed at the same time. Uninstall the old one before you download the new one.

Visit www.filehippo.com and look around. It's a very safe site and has a lot of stuff to download. Some are trials and some are free or shareware.
AVG Free
Avira Free
Bitdefender 10 Free
Avast Free

I kind of liked Avira myself but it had a conflict with mt file eraser, and would warn of a virus when I was erasing clean files so I gave it up. Avast is OK for an active scanner, but will ruin your downloads if it thinks there is something there even if it's a false positive, if you tell it to ignore it will still corrupt the file and you have to turn it off and re-download. Avast has a lot of false positves too. You should also be aware that some are On Demand Scanners and not Active Scanners which means its up to you to scan the files you download. But at least that way it will not mess with your downloads and stop them like Avast does. AVG a lot of false positives and can be a pain but it works.

When you decide what you want to try look on their site for any uninstall utility so you can remove one completely to try another. Or make a restore point to go back to after you uninstall each.

If you've got the resposibility to utilize an on-demand scanner oposed to a real-time scanner then I would suggest Malwarebytes (Malwarebytes : Free anti-malware, anti-virus and spyware removal download (http://www.malwarebytes.org/))

I recommend this: http://www.microsoft.com/en-ca/security_essentials/default.aspx

SuperAntiSpyware, Malwarebytes, PC Tools Free Antivirus, AVG Free, SpywareBlaster (prevention measure), Spybot S&D (Search & Destroy), SpywareDoctor.