Important Update: An issue affecting a small number of hubs has been identified that may cause this issue. To ensure your hub is up-to-date with the latest critical fixes, ensure the hub is connected to your router and that your router has internet. After powering up the hub, wait for 10-15 minutes. The issue should resolve itself through mandatory software patches. See here for more information regarding connectivity.
As the hub boots up, the lights will rotate and flash. Once the lights are stable and fully lit, you should wait 5-10 more seconds before clicking the discovery button. If the hub lights still do not rotate when pressing the button after the hub has been on for a few minutes then: