Nikon D3400 lent to girlfriend for Halloween. Now half of the live view image is totally black; same on photos but not on menu displays.
She "cleaned" it before returning, so is my sensor toast?
Looks like the shutter's getting stuck to me. I say that because the amount of visible photo changes between shots. It's simple enough to confirm too.
Look inside your camera. You should be able to see the whole sensor.
I suspect you'll only be looking at a portion of yours.
Fixing that probably means a trip to a Nikon Service Centre but —assuming it is a mechanical problem— other camera repair shops may be able to see what's wrong and fix it without spare parts. It may be (he said shuddering) a bit of cotton wool jammed in there. You may even be able to carefully remove the blockage yourself.
You've said Live View is similar so that adds credence to the above but you may turn it around and see the whole sensor. If it is at all intermittent —eg try a slow shutter speed, low light, etc— you might want to repeat step 3 but watch the shutter open. It's possible it's getting slowed down by gunge.
When people have to "clean" cameras before they return them, it might mean it's had a sticky drink spilled on it. I'd honestly expect to see evidence of that on the sensor but I guess we'll see.
What would make a borrowed camera require a cleansing before returning? Getting that question answered is likely to give you more of a clue about what happened and what remedies might be necessary than what you are working with now. Of course, there are also manners of cleaning that are detrimental to a camera: when you are trying to remove traces of substances gotten on the camera, it is rather likely that cleaning attempts will work diluted versions of the problematic substance into whatever unsealed openings might be available, actually causing the problems that the original spoilage did not yet produce.
So don't be coy and get that information. Finding the most promising way to salvage the camera may depend on it.
Your image looks like the text-book example of a flash-sync mismatch. This is when your shutter begins closing as the flash is fired.
Typically, you want the shutter to be fully open when the flash fires. This is know as the Flash sync speed. For your camera it is 1/200th of a second or less. Any shutter speed above this speed will close before the flash fully fires. You need to ensure that you have the shutter speed at 1/200th or less if you are using flash, even the one built-in.
In the first picture, this seems plausible, but the second appears to be outdoors? where the flash would presumably have little impact. In any case, try putting the camera in full auto (green) mode and taking the shots again, as the auto mode will force flash sync speed or lower.
See this site for example images demonstrating flash sync speed mismatches: http://www.wrotniak.net/photo/tech/fp-shutter.html