8 hours??? Are you sure? Can you access web interface of TL-WR841N before you access internet? What's the firmware version? Is it the latest version?

Did you try MAC Clone? If it won't help as well, report the problem here. http://www.tp-link.com/en/Support/contact/ By the way, the picture is too smal to see it clearly and the link cannot be...

Upgrade the latest firmware which should be140929 as it improved the compatibility with DLNA... After upgrade, reset it to factory defaults and reconfigure it....

Not sure if WDR4900 has such a security issue with IPv6. You may contact TP-LINK technical support to confirm. http://www.tp-link.com/en/Support/contact/

If the router from your ISP is a wireless one, to link the second one wirelessly, you can follow the guide as below to enable WDS on WDR3600. http://www.tp-link.com/en/article/?faqid=227

dyawlak wrote hi Yer both are enabled in dual band settings and both have their ssid enabled but only the 2ghz radio shows enabled and works fine. thanks So 2.4GHz wireless light is on but 5GHz...