DIAGNOSIS The router is stuck in its boot cycle. The ISP modem isn't handing off an IP address properly. This is a common handshake failure.
FIX Power off both the modem and router. Disconnect the Ethernet cable from the router's yellow Internet port. Wait 2 minutes. Power the modem on, wait for all its lights to stabilize. Now connect the Ethernet cable to the router and power the router on. Wait for the white light to become solid.
IF THAT DIDN'T WORK Log into the router's web interface at routerlogin.net. Go to Advanced > Setup > Internet Setup. If your ISP requires PPPoE, you must enter the username and password here. If you don't know, contact your ISP.
HEADS UP Never connect the modem to any of the four gray LAN ports on the RAX50. It must go to the single, separated yellow WAN/Internet port. A wrong cable connection causes this exact blinking light.