I had this same problem, but I tried on the computer that I actually bought my Macbook on, and it worked right away.. It even showed like 9 quantities in the order, meaning that the server got my order, but never showed me the checkout screen.
Anyone in the Uk, being able to process order, I had the same problem as original poster. Waited a day and worked fine, now it lets me qualify 3 machines, go to checkout and there is nothing in my basket.