Try the configuration here. http://forum.tp-link.com/showthread.php?82264-Blocking-Access-to-Internet

Is it still under warranty? Try to get a replacement from the retailer.

If you want to block all internet access, you can put in a invalid domain name like www.1234567.com. If you want to allow it access all internet, you can try to put . in domain name to see if it...

Upgrade the latest firmware. Reset and reconfigure it. http://www.tp-link.com/en/download/TL-WDR3600_V1.html#Firmware If the problem continues, on its web interface, go to IPv6 Support---IPv6 Setup...

What's the hardware version and firmware version of your WR940N? You may upgrade the latest firmware first. Did you try channel 1, 6 or 11 and channel width 20MHz? Change transmit power to middle to...

Did you try wired connection to WR841ND? Is it stable? How about status of network connection on your clients? Can you login web interface of WR841ND? What's the distance between the main router and...