Immediately after receiving the code for the Beta exam, I too tried to register on the Prometric web site. The site was not only slow but, was also acting VERY strangely. After signing in, and after having gone through several screens in the registration process, the site would send me back to the beginning and ask me to sign in again. Which was strange since I could clearly see that I was still signed in and there was a link available for me to sign out. This happened at least three to four times. Finally, after having tried for over a half-hour, I gave up and called the Prometric service center. Guess what? Their systems were just as slow and the representative who answered my call had to get her supervisor to put my request through their system. All in all, after an hour and twenty minutes, and having been put on hold four different times, I was finally registered for the exam and I am now good to go.
So for all of you out there, please practice patience and just remember, this will definitely be worth the "trouble" once done!! Good luck!!