5100 cn streaks down the middle of page

The printer either has a bad roller system, or the toner is leaking into the roller system.  I would have this printer serviced as soon as possible.

You could also have streaks because of a bad drum.  Or because of your transfer roller or fuser.  Can you describe the streaks better.  Also, you can go into customer mode by holding top and bottom arrows and powering on the printer.  There is a test print section where you can do individual sheets of the different colors as well as gradation prints.  On line, dell's site has troubleshooting wizards that will take you step by step through the whole process.  Or you could do an email chat with a dell technician as long as you are near the printer and a computer.  Just simply telling the poor user to have it serviced immediately doesn't seem very helpful to me:)