Call the Dealer who suppled the car and they should be able to give you the code over the phone. Number should be in the service book 
  
After a few wrong attempts I think it locks the hu 
  
You may need to take the hu out and give the serial number to Nissan to get the code - serial no is on the side of the hu iirc 
  
Read this ....'Turn the radio OFF,and hold in the "4" button and turn it back on'. As temp fix