The likely cause is that the mirror is locked up, so it is blocking the pentaprism from displaying the image to the viewfinder, on the other hand the sensor is able to have an unobstructed view.
What lenses were you using when this happened?
cheers, TREVOR
The mark of good photographer is less what they hold in their hand, it's more what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
