Please check the following points:

• You may clear the problem by cleaning the primary corona wire inside the drum unit by sliding the blue tab.Make sure to return the blue tab to the Home position. To see how to clean the corona wire of the drum unit, click here.
  
• The toner cartridge may be damaged. Put in a new toner cartridge. To see how to replace the toner cartridge, click here.
• The drum unit may be damaged. Put in a new drum unit. To see how to replace the drum unit, click here.
• The fuser unit may be smudged. Call Customer Service.