DIAGNOSIS The router can't establish a connection to your modem or ISP. The blinking orange Internet LED specifically indicates a WAN (Wide Area Network) link issue, which is usually a physical or configuration problem between the router and your modem.
FIX First, power everything down. Unplug both the modem and the router. Wait 30 seconds. Plug the modem back in and wait for it to fully boot (all its lights should be stable). Then, plug the router back in. Ensure you're using the included Ethernet cable and that it's firmly connected from the modem to the router's yellow Internet/WAN port. Give it a few minutes to negotiate the connection.
IF THAT DIDN'T WORK Log into the router's web interface (tplinkwifi.net) and check the Internet Connection settings under Advanced > Network. If your ISP requires specific settings like PPPoE (common with fiber or DSL), you'll need to enter your username and password there. If you're cloning a MAC address from an old router, try disabling that feature temporarily.
HEADS UP Some modems, especially cable modems, can 'lock onto' the MAC address of the first device connected after a reboot. If you swapped routers, a full power cycle of the modem (unplugging it for a full minute) is often necessary to clear that lock.