virtualization - How can I grab license-key from my pre-installed OS and use it to activate a virtual machine?

So I'm having problems virtualizing my preinstalled OS (yes it came already installed in this laptop), and I'm thinking of giving up: just starting the virtual machine from scratch, installing Windows8 from a CD from a friend.

If I were to do this, how can I grab license from my pre-installed OS and use it to activate a virtual machine? (If I didn't try to do this, I would be using the license of my friend, which would not be legal/feasible I guess.)