Inkjet cartridge nozzles can become clogged, especially if not used for a while.  You can try this procedure and if it doesn't help, new Dell cartridges are probably needed.  Soak the nozzle end of the cartridges (one at a time and in clean water for each cartridge) in a shallow container of warm (not hot) water for about 10 minutes.  Blot the cartridge dry (you should see some ink on whatever you use to blot it dry), reinstall and try a print.