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An LCD-type display may either have 'gone dead' i.e. ceased displaying/interpreting any input data to it at all... or else it may simply have lost its backlight. If you are uncertain, shine a bright light into the display to see if anything is visible that way, and if nothing is, the LCD display itself is defective - or else at minimum, its cable has come loose (not usually, but sometimes.)
Most likely the display portion will have to be replaced. It's a common enough problem.
(This only applies if the FBX works properly otherwise. If it does not, or if there is no way to verify its continued operation, a problem of a broader extent may be what is wrong, not just the display... e.g. lack of central control circuitry initialization, or power supply failure, etc.)
If you would like to have the FBX device repaired, please let me know your zip code, or other locality indicator such as town/city and state or region.