Need help with change address not functioning, losing customers!

I'm working on a site for a client who is using Zencart, they had purchased a slighted outdated template which I think may be affecting the installation. Basically, in the website, nobody can seem to change their address. This is a huge problem and people are not fulfilling orders they intended to fulfill because of it.

http://www.whyrentbooks.com

Also, problem number two, when going from step 2 to step 3, the confirmation, it keeps kicking them back to step 2 with no error messages! What files do I need to restore from the clean 1.3.7 to make this work? Fyi, you can't currently test problem two on my site because I had to disable the credit cards.

Update:

"You must select a country from the Countries pull down menu"

This shows up when trying to edit address from step 1 of checkout process. Editing address in my account simple returns the same page with all blank textboxes.

Help! I'm losing 10 customers per hour!!

Thanks to those who may have looked at this thread, but I should've read around some more...

http://www.zen-cart.com/forum/showthread.php?t=49121

The files I updated were:

tpl_address_book_default.php
tpl_address_book_process_default.php
tpl_modules_address_book_details.php
tpl_modules_checkout_new_address.php
tpl_modules_create_account.php

I don't know exactly which one did it, but I'm sure if anyone has this problem that this will work.