Before doing a factory reset, which will delete custom settings, try to reboot your Wi-Fi gateway.
Heads up: Be sure to jot down your custom settings, like your static IP address if you have one, or your Wi-Fi® network name (SSID). You can then change them back after the factory reset.
If you still have problems, make sure your device isn’t defective. Find out what the status lights on your gateway or modem mean