When I attempt turn wifi on a device, I get a message saying I need to sign in on the login page. The login page won't load, only gives an error message.
Are you referring to inputting the WiFi password? If not, can you describe the login page you're seeing? Even better, could you provide a snapshot of it?
Also, was it a phone rep who told you to reset the modem?
If you have a LAN cable connected device, are you able to access this modem page? If so, what are you seeing for both the State Code in the System Summary box near the top and the Satellite Receive Signal Strength in the Wan Info box on the bottom left?