D7000 has very dark video

I teach at the University of Missouri, I have three students in Central America working on a project. They just called to say that the one of two D7000s they took has been recording their video darker and darker. It's at the point the video can't be used. Wonder if anyone know what might cause the problem? It is very hot, so I believe it's related to the sensor as the card works fine in one camera but not the other. Any suggestions? And if it's the sensor or camera, will it heal itself if not used overnight? Thanks

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Thanks
The first thing I would have them do is to do a factory reset to get rid of any incorrect setting someone might have accidentally made.

You can find the details here

https://support.nikonusa.com/app/an...-to-reset-a-d-slr-to-factory-default-settings

D7000 with what lens? Using the kit lenses, as you zoom in or out, the aperture will change since the lens has a variable aperture. What ISO were they using? Typically, you need to shoot in M mode, 1/50, ISO can vary from 800 - 3200.