Your description on setup is not clearly enough. Your modem and router are connected by powerline devices or ethernet cable? From router to NAS and from router to PC are both connected by powerline...

Why??? Is it normal to happen? When it recovers, you can access internet but ip address with my hosting address is not updated?

Are you trying to use it as an access point or something else? Without TD-W8980, how did you access internet?

Real IP refers to WAN IP? We cannot do that. If you restore the device to factory defaults, it will be in bridge mode. If you set up PPPoE connection on PC, you can obtain a public IP on your PC.

Can you make changes to the account? 1. Control panel -> User Account and Family settings ->Add or remove user account. Click on Manage another account and choose the account which need to be...

Did you check VPN and dial number with your ISP and try to manually configure it? If it is the same, report it here. http://www.tp-link.in/support/contact/