Possible reasons for a Box to be offline are:
- no power
Make sure the Box is plugged-in to power.
- no network connection
Verify that you see sporadically blinking light on the Box's Ethernet port and that you can see the Box's MAC address on your local network.
- invalid network configuration
If you accidentally assigned a manual network configuration that's incompatible with your network (e.g. gave it an incorrect static IP address, gateway IP address, or DNS server), then perform a factory reset.
- hardware failure
To diagnose whether the Box hardware itself has failed (e.g. bad disk), you can plug the Box into a monitor via the HDMI port just to see whether the Box boots when you re-power it by observing the system startup messages.