The cause of this problem usually has to do with your display. Please check:
1. Make sure the source on your display didn't switch.
2. Make sure the display is plugged in properly and has power.
3. Make sure your Media Player is plugged in properly and has power.
4. Make sure HDMI cable didn't get disconnected.
Unplug the power of your display/media player and plug it back in. Log out of your Wondersign account and back in to make sure the device says "Connected."
Please contact firstname.lastname@example.org if the problem persists.