Re-install question

I just have a question about re-installing the 777. I bought the 777 when it came out but recently ran into performance issues with FSX that I wasn't able to resolve, and in the end I decided it was best to do a complete re-install of FSX - this isn't such a big deal because I have so few addons.

So after I went through the process and everything was set up again, I installed the 777, but this time it didn't ask me to input my activation key. I read (I think in an article on PMDGs website) that if you don't completely uninstall and delete everything before a re-install of your addons you could run into problems. If I had uninstalled it correctly would it have asked me to enter the activation key again? 

I may sound a little paranoid, but it's is because I'm obsessed with performance, and when a loaded up the 777 for the first time on the new install it seemed a little unstable, and the second time I had a CTD. I never had a single CTD in the time I had it until now. 

What do you think?