After taking the picture it is customary to set the camera to display the thumbnail of the picture taken for a few seconds. In your case someone has changed the settings in the Menu and you need to change that. (I have the Nikon D70S).
Here is the manual:
http://www.nikonusa.com/pdf/manuals/dslr/D70S_en.pdf
The Menu changes are straight forward, and in any case you need to be familiar with the settings.
Good luck!