If cleaning the sensor did not help, then you can try the troubleshooting steps below:
Make sure the battery is fully charged and that you are using an approved memory card.
Turn off the camera, remove the battery and the memory card, wait a few minutes, replace the battery and the memory card.
Remove lens and accessories from the camera and reattach, then turn on the camera.
Reset the camera back to the default settings - see the owners manual for instructions on this.
If the problem persists then you will have to send the camera in for service.
For instructions on how to send your item in for a warranty repair please see: http://support.nikonusa.com/app/answers/detail/a_id/336
The repair can take roughly about 7 to 10 business days from the day you receive your service order number to repair your equipment as long as there is no hold on parts.
For info on the Nikon Digital Imaging Warranty, see: https://support.nikonusa.com/app/answers/detail/a_id/333