If vBulletin.com is down for you all of the time then your IP has accidently been blocked. Which means you need to email
support@vbulletin.com saying your situation.
Obviously this is more awkward for you as you are not yet a customer but things should work out ok
It knows if your board is a legitimate one because you must enter your boards URL over at
www.vbulletin.com when you sign up.
Obviously they have a system to check if people are using boards illegally etc but i wont get into that