Here is a instruction on how set up the 5210 as an repeater, hope this can help: http://www.tplink.com/en/article/?faqid=348 5210 only allows WEP security. Make sure that your main wireless router...

This indicates that some information you put in is not correct. Your username form ISP should be like a E-mail address. VPI/VCI, connection type, username and password, all these information are...

How about connect the computer directly to one of the Ethernet port and the VOIP? Can they work at the same time? I think that the router made a limitation to the share the Internet.

It is not a good choice to connect the plugs into extension socket because it will slow down the speed or even can not work at all. Some extension will block the data that transfers through...

The Utility shows the quality is good? The download speed is tested by speed test website? How about download a movie from web?

How about reset the tl-wa5210 and then try on another computer? What is more, you can also try to ping the IP address from the computer or check whether the IP address is correct or not.