This happened on my D800 recently, mirror stuck up, couldn't see through viewfinder, would take pictures but part of the frame was dark, live view operated normal and pictures did not have the dark area on the frame suggesting the shutter itself was fine but some other component failed.
$300 and Nikon replaced the shutter & aperture assemblies (see picture, I kept the old parts).
On a D80 I'd probably get a new camera as opposed to fixing it, assuming it is the same issue.