So confused by your description.

There is only one Ethernet port on TL-WA701ND, so there is no division of WAN/LAN port.

Sorry Simon I write it wrong it is WLAN. I also correct it. So what should b the problem

i have the same proplem of you
after a long long search i found the solution finally
1)
you need to reflash you access point using openwrt
search google using openwrt + your access point model
or you can find the thread here
http://wiki.openwrt.org/toh/tp-link/tl-wa701nd
2)
another solution is to use the small memory chip called (spansion) from another working access point of the same model .
then power up the access point it will load the firmware from this chip
then turn off the access point
after that you can use the old memory chip and solder it again
i know may explanation may be not sol clear
if you can read arabic language then you can read the full solution from here
http://mikrotikarabic.blogspot.com/2013/11/tplink-701-vs-741.html