failolai

Hi all, I installed Prestashop on a Synology NAS. It works fine for both the shop and the admin in local network. (http://192.168.1.3/prestashop and ...../admin) However when I attempted to access the Pretashop from internet with the ddns provided with the Synology (???.synology.me/prestashop), it stops for a while and then the web address changed to http://192.168.1.3/prestashop and shows error. I put a trial html file in the pretashop folder with try.html, ???.synology.me/prestashop/try html works properly. I had open the port 80 for webserver already and I had sucessfully access the webserver (???.synology.me) and the photostation (???.synology.me/photo) of the Synology NAS from internet. Do I need to open other ports or do other things? Please assist.