Windows Activation for systems not purchased with an operating system

I didn't purchase Windows with my new system because I already own a copy. I assumed when the system arrived it would have no operating system however it came with the operating system used for testing. As it was the same version I have (Windows 7 Home) I assumed I could just activate it using my code, however the activation application will not open. After searching around a bit the solution appears to be to re-install completely which seems ludicrous. Is this something you've encountered before and if so do you know of a way around it without having to do a full re-install?

Have you tried one of these methods?

I'd tried the GUI route and nothing happened, not even an error. However I hadn't tried the command line route and that worked perfectly. Thanks!