@Twey 

Hi,

First make sure that the Ethernet cable going from the TL-WR840N router's "WAN" port to your home's Internet source is seated properly. If you have another spare Ethernet cable available, then try if replacing the cable makes any difference.

If that doesn't help, then your type of Internet connection likely requires the TL-WR840N to be specifically configured for it. You can consult the User Guide and the Setup Videos on your router's TP-Link support website on how to do that.

https://www.tp-link.com/en/support/download/tl-wr840n/v6/