Hi, I am A. Stevens here to help with your question! Can you try a direct connection from your modem to your computer to ensure your WAN connection is active?
Great, just wanted to rule that out as a problem. Did you set up the Airport Express in the past? Just want to ensure your ISP does not require any additional information to be entered on the router to access the wan connection
Can you let me know which generation Airport Express this is?
Also one more thing, have you tried restarting or resetting your modem?
Right, I understand. So had you tried resetting your modem yet?
Does your modem have a reset button on it that will restore the modem to factory default?
Let me locate that model and see if I can find a method to completely reset it
Management interface address assuming you haven't made any change to the default.