DIAGNOSIS A solid amber power LED means the router has booted but can't establish an internet connection from your modem. It's stuck in a "I'm alive but lonely" state.
FIX This is almost always a modem/router handshake issue. Power cycle both. Unplug the router's power, then unplug your modem's power. Wait 60 seconds. Plug the modem back in and wait for all its lights to settle into their normal state (this can take 2-3 minutes). *Then* plug the router back in. Make sure the Ethernet cable from the modem is plugged into the router's blue Internet port, not one of the yellow LAN ports.
IF THAT DIDN'T WORK The cable might be bad or the modem needs a release. Log into your modem's interface (if you can) and release any DHCP lease. If not, with everything powered, unplug the Ethernet cable from the router's Internet port for 30 seconds, then plug it back in firmly.
HEADS UP If you just switched from an old router, your ISP might need to reprovision the modem for the new router's MAC address. A call to them might be necessary, but the power cycle fixes it 90% of the time.