2,4ghz network not visible on sbg8300

Is the 2.4 network was working before or its stopped working?

If your are using default Wi-Fi credentials please change it and try connecting to the new Wi-Fi network name if still not working you need to perform hard reset on the modem to check on this further. But after resetting the modem will go to default setup any custom settings will be removed so use the default network name and password  to connect to your network.

http://arris.force.com/consumers/articles/General_FAQs/SBG8300-Changing-the-Wi-Fi-Name-and-Password

http://arris.force.com/consumers/articles/General_FAQs/SBG8300-Factory-Reset