Diagnosis
This is a boot loop or a corrupted startup process, most often triggered by a failed software update or a power interruption during boot.
How to Fix It
Force a restart. Unplug the Cube's power adapter from the wall for two full minutes. While it's unplugged, also unplug the HDMI cable. After two minutes, plug the power back in first, wait for the white light, then reconnect HDMI. This clears the system cache and forces a fresh boot sequence.
If That Didn't Work
You may need to perform a factory reset. Press and hold the Back button and the Right side of the navigation circle on the included remote simultaneously for 10-12 seconds while the Cube is on the logo screen. This should initiate the reset menu.
Heads Up
A factory reset will erase all your apps, logins, and settings. You'll have to set it up again like a new device.