Windows XP Product key?

MY computer recently crashed and went to a repairguy. ( A friend of my dad fixed it) Now since the computer crashed he put a new hardrive and basicly most of the files are missing. So i was trying to reinstal Mcafee and IT said my software product(windows) is out of date and need to be updated. So i go on windows updater and it says my product is not genuine.
I go on my computer and i click properties and i see the Registered to: section got changed and had the repair guys name. SO now the PRODUCT KEY IS CHANGE AND WIndows thinks its now a fonny any ideas on what to do

I originally got McAfee free through AOL a few years ago, and I always got the free updates and stuff for years. Now I reinstalled Windows, and I want to get this McAfee back free. Anyway I can use the backed up files to do this???

Virus Protection?

We are a small firm, 10 seats, and currently use Norton Anti-Virus and are sick of it. Problems with existing applications and an administrative nightmare. What are the other options? What do other people use for virus protection? I looked at mcafee and it was even worse. What do the big boys use for virus protection? Thanks.

if im getting the same company’s virus protection again, do i have to uninstall the old one?

like lets say you have mcafee and you get another mcafee but a different version. like internet security or 360.

and im thinking about getting a cd, not renewing it online

I used a thumb drive and installed Malwarebytes onto my laptop and it removed the Antivirus 2009. Now I can surf the web, get windows updates and things I couldnt do before. But, when I go to get Mcafee from comcast something blocks the page from being viewed. How can I get around this to access virus protection?