DIAGNOSIS A solid amber light on the internet port means it's detecting a physical connection to your modem but isn't getting a valid IP address from it. It's a handshake failure.
FIX Power cycle the whole chain. Unplug the router AND your modem from power. Wait 30 seconds. Plug the modem back in and wait for all its lights to settle (usually 1-2 minutes). *Then* plug the router back in. Let it boot for another minute. The internet light should turn white if it worked.
IF THAT DIDN'T WORK Try a different Ethernet cable between the modem and the router's yellow WAN port. If that's not it, you may need to release the old IP from your modem. Leave the router unplugged but the modem on for 5-10 minutes, then reconnect everything.
HEADS UP If you're replacing an old router, some ISPs lock the connection to the previous device's MAC address. You might need to call your ISP and tell them you have new equipment so they can refresh the connection on their end.