Is your router using the latest firmware? If not, you'd better upgrade it first. Here is an instruction on how to upgrade TPLINK routers: www.tp-link.com/en/article/?faqid=296.
Then go through the "quick setup" process on the router's configuration page: choose "3G/4G only" as "internet access", then choose your location and mobile ISP.
With these done, reboot the router and wait for about 3 mins and check if the internet works.

Matthew cook wrote

Is your router using the latest firmware? If not, you'd better upgrade it first. Here is an instruction on how to upgrade TPLINK routers: www.tp-link.com/en/article/?faqid=296.
Then go through the "quick setup" process on the router's configuration page: choose "3G/4G only" as "internet access", then choose your location and mobile ISP.
With these done, reboot the router and wait for about 3 mins and check if the internet works.

Hi Methew,

I am from India and was using MR3020 successfully till yesterday on my broadband connection. Unfortunately i downloaded firmware (TL-MR3020_V1_120817) from below link and i upgraded firmware but after few minutes it showed restarting process and it restarted. When i power off/on router, it did not get connect to my laptop, how ever wifi detect router but when i am trying to get connected, it gives message - Window unable to connect TP-LINK MR3020 ........." Can you please help to resolve this issue which has occurred after firmware upgrade.

http://www.tp-link.com/en/support/download/?model=TL-MR3020&version=V1#tbl_j