Hello Rose

                   We understand that you are having issue with Wi-Fi connection on SBG8300, since the direct connection that is hardwired devices are working fine we need to first confirm the light status on the modem and whether you can able to see the Wi-Fi name on any of your devices to connect to the network or not, if you are able to connect to the network without internet we need to test the modem further. You can try basic trouble shooting like restarting and resetting modem without coax for 30secs. Please follow the steps mentioned on the below link to perform reset on the modem.

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

               After the factory reset, the modem will go to default setting and any custom settings will be removed so use the default network name and password to connect to your network.