I have a Nikon D90 that had an unfortunate fall. Since then, if I have it in any mode except manual it throws up an Err.
If I use it in manual and follow its exposure guide in the view finder it vastly over exposes (white). However, if I ignore the exposure (let it say the exposure is way too dark), best guess then adjust based on the preview for that pic, it works.
So it seems the either: a) the exposure sensor is broken; b) that the sensor isn't actually being exposed to light through the lens and is only, eventually, being exposed to some incidental light through the view finder - hence the white out; or c) something in the electronics that interprets the sensor.
Given the autofocus still works (in manual) and I can see through the viewfinder just fine I assume the mirror, focusing screen, and autofocus sensor are all functional. But the fact that it does eventually read some light suggests it is still 'on'/responding/plugged in, perhaps?
Can anyone think of anything else I could try before I try before attempting to get into the prism? :s