And now, help me with my router.

[Adrian's Dome]

I have an Apple AirPort Extreme (newest one with the b/g/n/ac.) Previously I'd been using it with a bridged Motorola SBG6580 with zero issues.

Moved and left the 6580 behind. Bought a new Motorola plain cable modem. New house was pre-wired so I got the Comcast self-install kit and set the internets up. Modem works and anything hard wired to it via Ethernet cable works (laptop, PS4, etc.)

I reset the Extreme and connected it to make a wireless network. It shows as a new unit in wireless networks ready to be configured. When I open up AirPort Utility so I can configure, it finds the Extreme and attempts to connect to it, then gives me a "An error occurred. Please try again."
message. The extreme won't broadcast any wireless network but it's there on all devices wirelessly ready to be configured, all give the same error message.

I googled the issue and found something about changing the IPv4 settings, tried it to no avail, same problem persists.

Is this a hardware issue with the router or something with the modem not being able to communicate with it?

 

[Adrian's Dome]

Figured out the problem. If anyone else experiences something similar, my modem is a Motorola SB6121, and when you initially configure it manually via ethernet (which I did,) the modem "learns" the address of the first device it's connected to (which was my laptop,) and won't send out an IP to anything else.
 
A full power cycle to make the modem "forget" the laptop and connecting it directly to the AirPort Extreme before powering it back on immediately fixed the issue.