Just try to activate online and it will probably fail and tell you to activate over the phone. It's am automated system. If it detects it's been activated more than once the system will ask how many systems it's been Used on. Just say 1. It will continue on and just follow the prompts. I've only once ever had to talk to a live person, and that was while I was working at a shop and reformatted a system and they were using a pirated key of XP.
Sent from my HTC One
Sent from my HTC One