Most of those probably have florescent back lit screens rather than the newer LED back lighting.
LED devices with the older technology have a limited life, in comparison. I have seen over a dozen older LCD monitors die, after about 8 years of daily use. They may start to flicker, may turn off after a while, or may have a purple tint at the top and/or bottom of the screen. You can usually shine a flash light, when the device is on, to see the image is actually there. (even though it appears to be dark/off).
The newer LED stuff should last many times longer, using very little power, and will be much brighter.
The same advice applies to computer monitors, flat panel tv's, etc. LED is the way to go
In the case of what the customer has, I think those are meant to be disposable. Hopefully the images are on a flash drive and can be recovered.
Mike
PS: It could also be the external power supply, if it was hit by a power surge.
PPS: This answer was probably more than you wanted to know.
They should have framed it properly to begin with