You can use AirPort Utility to tell you exactly why the AirPort is blinking amber and suggest a fix.
Assuming that you have a recent operating system installed on your Mac......
Open Finder > Applications > Utilities > AirPort Utility
Click on the AirPort icon
Look for the setting for Status and click on small amber dot there for a message to explain why the light is blinking and a suggestion to remedy the issue.
A guess on the issue would be that your ISP sent you a new modem/router when you had a simple modem previously.....and the AirPort detects another router on the network, when you only want one router on a network.