If your win 7 is genuine/legitimate and have lost the key then 'belarc advisor can easily find it for you.
http://www.belarc.com/products_belarc_advisor
install and run it, scroll down to find your windows product key
you can download the iso for windows 10 from windows and burn on to a cd, then use that as a install disk from scratch using your legitimate windows key that you now have to activate it. (when activating, sometimes you might have to do it by phone but it is easy.)
then install vrc pro which is the only reason for having a half decent pc.
good luck
Phil