No image, glowing black screen
If you have a glowing black screen (back lit LCDs) then 99% of the time the LCD driver is functioning correctly and its an issue with either the camera or video feed (if no video, the screen will appear blank).
If no image in wireless mode (should see snow):
1) Receiver not installed or seated correctly (modular goggles). Check to ensure receiver pins line up to socket.
2) Receiver not turned on (switch is located on bottom side of goggles on the SMA side).
Note: Make sure transmitter is turned off when testing. If changing the channel causes snow to appear, then you are receiving a blank image from a transmitter.
Snow with transmitter off, blank with transmitter on: Goggles are functioning normally. Likely cause is a faulty camera or incompatible camera (alternative brand cameras may require 12V and have different pin out on the connectors - Fat Shark transmitters supply 5V).
No image wired mode: Most likely not using Fat Shark compatible A/V cable (3p prong pin out configurations are different for different manufacturers - they may look the same but are wired differently)
Image for split second then fades away: This usually happens when connecting to gaming systems. The problem is the source device is outputting a Progressive Scan video. Fat Shark goggles only support Interlaced video.