ETHERNET WORKS BUT NO WIFI

Great ethernet connection but no wifi. The wifi indicator on the modem is lite but when searching for wifi on my phone or laptop routers name is not available. I've reset the modem, I've disconnected the power and unplugged everything for 15 mins. After rebooting the router name appears on my phone and then disappears not to be found unless I reboot it, in which then it goes away again. I did notice on my phone it's says obtaining ip address for about 30 secs then it disappears. I can't even log in to the router. PLEASE PLEASE HELP