If you are trying to use iTunes on Windows and you can’t, you may have to disable your firewall. Seriously! I tried a number of things, and I finally came across this, Resolve issues between iTunes and third-party security software – Apple Support, as well as some other sites, and once I did that, I was able to get it to work.
If you are unhappy with that, your next best option is to methodically follow this and poke enough holes in your firewall to work. That’s the safer route, by far.