If none of the devices are able to see the network names.
I would recommend performing a network reset through the web-based interface (GUI).
You can do this by navigating to Troubleshooting > Restart/Restore and then selecting 'Restore Wi-Fi defaults.
Additionally, you could also try changing the Wi-Fi channels to see if that resolves the issue.
Please refer to the link below, where you can find the instructions on changing Wi-Fi channels
http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Changing-the-Wi-Fi-Channel
Also try enabling the guest networks to check if they are broadcasting.
I tried all the above and I am still having issues. I moved the router to a new room and placed my phone on the modem. Only when my phone is directly on the modem do I get wifi access.
While adjusting the Wi-Fi channels, could you also try changing the bandwidth settings? This can sometimes help improve the connection.
For the 2.4GHz network, if the bandwidth is currently set to 20MHz, please try changing it to 20/40MHz. Similarly, for the 5GHz network, you can adjust the bandwidth to 20/40/80MHz. Additionally, it may help to toggle the setting.