I think you can disable the Hardware NAT to give a try . Go to http://tplinklogin.net,NAT-->disable the hardware NAT.

I think you can disable the HARDWARE NAT on TP-LINK and then do the IP&MAC binding.

After you upgrade it, have you reset it? I think it should under the menu Network-->WAN as normal one.

I think you can change the router's wireless 2.4G security to WPA-PSK/Personal AES. The default setting on the router is auto for the WPA-PSK/WPA2-PSK.

Is it for wireless connection or wired connection? For the wireless, i think you can try to change the channel to 6 for 2.4G. Disable the Hardware NAT would also be an option. For the wired...

Go to this link and make the router work as an AP: http://www.tp-link.com/en/article/?faqid=417