@Stanmiko 

The fourth one should be the internet light, and it needs to be green when connecting to the internet fine. So in your case, you may check if the WAN/internet cable is plugged securely, be sure your modem is generating the internet fine, then contact the tp-link tech support if the internet is still not working properly on the router.

This is the basic troubleshooting when the router is not connecting to the internet properly, you can also check:

What should I do if I cannot access the internet through Wi-Fi router?