AirPort Express

Can you still find the Airport Express via airport utility? If not do a hardware reset and start over .. this is the easiest way generally regardless.

I assume you are running it in join a wireless network mode..??

You may need to do a bit of fiddling to get it working .. but try auto setup from airport utility after the reset and tell us how it goes.

Chances are, you had the AirPort Express configured to join your previous Wi-Fi network supplied by another Internet Service Provider (ISP), correct?

If yes, the AirPort Express is still "remembering" the settings that it used to connect to your "old" network.....and it has no idea that you have a "new" network. So, the Express is lost, and it does not know what to do.

If our guesses so far are correct......you need to do the following:

1) Perform a Hard Reset on the AirPort Express to erase the "old" network settings

2) Set up the AirPort Express again using a Mac or iPhone to join your "new' network

Post back if you need a few more tips or details on this.