The screen will give a phone registration method if you can't do this online. As it's a big world, I won't list all the numbers here.
I bought Win7 and tried to install it on my older desktop computer but the install "stalled" and after several attempts and hardware modifications I gave up.
Now, I have reinstalled XP. How do I register my old XP?
The program will only run for 30 days if not registered.