Restart your modem.
Restart your router.
Do a hard restart of the XboX One.
To perform a hard restart, hold the power button for 10 seconds while the system is on. The system will turn off. When you hit the button again, it will start and display the green start-up screen.
All your data is preserved, but cache is cleared and some settings are reverted and log-in or game start issues are resolved.
Alternatively, you can perform a full shutdown by going to SETTINGS / POWER & STARTUP and change POWER MODE from Instant-On to Energy-saving. After changing the setting, choose "Turn Xbox off". It can be powered back on by holding down the GUIDE button on the Xbox controller or the button on the front of the Xbox console. Once it's back online you can go back to SETTINGS / POWER & STARTUP and re-enable Instant-on.
NOTE if the manual button/menu-initiated reboot doesn't work, do it the old-fashioned way: power down the Xbox One, unplug it, wait for 10 seconds, plug everything back in and power it back on.
