@Tonixxx 

Try if it makes any difference if you enter the whole address into the browser's address bar. Like http://tplinkwifi.net instead of just tplinkwifi.net.

If that does not work either, then try http://192.168.0.1

I tried it already, http://tplinklogin.net . http://tplinkwifi.net , the default ip http://192.168.0.1, but still it had the same result.

  @Tonixxx 

Try using another device. Anything that has a web browser could be used to access the router's web interface.

If you still can't get in, then install TP-Link's "Tether" app on an Android or iOS device. That way you can log into your router without any browser. Once you are logged into the router, I suggest you check the firmware version of your C5400 and in case the firmware version is a rather old one, then update your C5400 to the latest one available in the hope that the "Unsupported Browser" problem may be something that has been solved already.