airport express router

For starters, this tells us that you do not have an AirPort Express......you have an an AirPort Extreme. Are you saying that you have both an AirPort Express and an AirPort Extreme?

Have you powered off the AirPort, waited a few seconds, then powered it back up?

Hi, welcome to the Apple Users Community.

Check the power cable of your Airport Extreme and that it is securely connected to the back of the unit and to the wall.

Best of luck

Yes, it is a wireless router