I'm having trouble setting up an archer

c 50(ac1200) router. I'm setting it up on an existing network as an ap and IV installed two other archer c50 routers on the network already(both working perfectly for 2 weeks now) but the third one won't connect to the network switch or a computer via ethernet cable(iv checked the cable and tried a few from other devices). Sorry for the long post just trying to give all the details. 

When the router boots up all the lights show up as they did on the other routers.

The power and WiFi lights on the router light up after that but the ethernet light doesn't. 

WiFi is working on it and I can login and changed settings are held by the router. 

When I loop the cable back into the router(et port1-4 or 2-3) the ethernet light flashes every 8 or 9sec. 

My pc shows its connecting then identifying network then network unplugged. 

I can get results off an ipconfig cmd when I execute the command right after my pc says identifying not after that. 

Iv reset to factory settings, set a static ip(that I know is available so its not an ip conflict) and tried leaving it as dynamic.

Iv turned the dhcp off when connecting to the network switch and left it on when just connecting to my pc with no change(multiple cycles and factory resets). 

Iv tried 3 different pc's direct to the router and wasn't able to connect. 

The original network was up for a few years and Iv just upgraded the wireless ap's to archer c50's all just out of the box and the network switch is also a tp link.

Any help would be much appreciated.