Any WAN IP obtained on web interface of WR740N? You are sure internet works directly from modem ot PC, old router disconnected? It seems that you haven't tried to change LAN IP....

I followed the instruction below and it works. http://www.tp-link.com/en/article/?faqid=227 :) Any MAC filter rules enabled on WR841ND v7? If MAC/IP binding is disabled, does the laptop connected to...

Sounds strange. How did you test W8980 has been cofigured in WDS mode successfully? With cable plugged in W8980, any IP address obtained on your PC? Default gateway is IP address of Tg582n?

Wired connection to C2 still works when Wi-Fi drops? Signal stength drops also? Can you login the web interface wirelessly? Try channels 1, 6 or 11. Sometimes it helps. Disable WMM. Also, you can...

Maintenance---Diagnostics---Online Detection Give a try there.

Reset them and make a network name for both to ensure it is a private network.