Make sure the Netgear EX7700 extender is in range of your wireless router. Make sure ethernet cable are properly connected. Reset the extender to its factory default settings, and try setting it up again from scratch. Make sure you are entering the correct Network name and password for your wireless network when prompted during the setup process. Update the firmware of your Netgear EX7700 extender to the latest version.
Did you set it up using the push button WPS option? If so, factory reset the extender and set it up using the installation assistant. To factory reset, push and hold the reset button for 7-15 seconds while powered on. Here's a video of how to use the assistant. https://www.youtube.com/watch?v=yJVklshxBMk
