I just made one more test and it looks like your home page goes down for some reason.
Your home page is blank
https://secure.cdworlds.com/cart.php
but admin page can be opened:
https://secure.cdworlds.com/admin.php
Could you please let me know if you have any errors in the <X-Cart 5>/var/log folder? If it is empty, can you please look into Apache logs and let me know if there are any errors there?
Tony.