Please check the following points.

• Make sure that the toner cartridges are installed properly.
  Please refer to the instructions, "How do I replace the toner cartridge?".
  
  
• One of the toner cartridges may be damaged. Identify the missing color and put in a new toner cartridge for the color with the white line.
  Please refer to the instructions, "How do I replace the toner cartridge?"
  
  
• The drum unit may be damaged. Put in a new drum unit.
  Please refer to the instructions, "How do I replace the drum unit?"