With Windows, you should not have to deactivate anything. When they ask why do you need to do this, I usually say "I've upgraded some hardware" which, if you do it enough, causes the anti-piracy technology to kick in and invalidate the current license. The only thing you need to worry about with other software and activation is software that activates via the internet. Of all my PC games, perhaps six uses internet authentication and those are newer games. Your antivirus sofware, if the license was for three PC's, may need to be repurchased since you've used the licenses already, or, you could use the free and very capable Microsoft Security Essentials
, which is what I use. I say install everything and don't worry about licenses until the problems, if there are any, come up. Chances are you have very few titles that would need re-authentication.