Subscribe buttons no longer working

Hi,
I had all my subscriptions and access levels working finally, but now when I go to my "Join Now" page and select one of my subscription packages, where it used to go to the payment page, now it just refreshes the page and url changes from:

http://ia.sitesee.ca/join-now/

to

http://ia.sitesee.ca/join-now/?action=registeruser&subscription=4

But that's it. It's just the "Join Now" page which lists all our available packages and the buttons lead no where now? What could have changed to make this stop workings?

Client is very anxious to put the site live asap, and I thought we were almost done, but we obviously can't do that till we get this sorted out. Thank you for any assistance you can give. Please let me know if you require access to the site and I'll turn it on for you.

Thanks!