I'm with you, I hate the ribbon, and there is an add-on I once used to restore the old menu. That ruined it for me as well. I use 2010 mostly now, which of course has the ribbon, but I put up with it.
I have the key that came on the original packaging ...
BUT once when I was looking in the Explore file manager, I THINK I noticed that the key was the serial number. So if you have it loaded on another system maybe you can find the serial number and try that.