Sounds like you had the same problem I had--
On the 'splash screen' when you start the game (where it asks you if you want to Buy Now, or continue with the demo), at the veryveryvery top of the screen, is 'Customer Support' in red text.
Click that, enter your order number and password, and it'll unlock the game for you. ^_^
(It still doesn't tell you your serial number though, but hey, at least it works)