There's a delayed exposure mode you likely have set. I believe it's in the menus, but have you tried moving the drive mode lever on the camera to see how it reacts?
Copyright © Nikonians 2000, 2013
All Rights Reserved
Nikonians®, NikoScope® and NikoniansAcademy™ are trademarks owned by Nikonians.org.
Nikon®, Nikonos® and Nikkor® are registered trademarks of Nikon Corporation.