Black and white is the most used colours while printing. They are the two most important colours of printing, and the two most 'early exhaust' colours. If you face a situation, where you might not be able to print black and white printers then first check the status of the cartridges. If they are down, then change the cartridges. If it's All right, then set the settings and try again. Also, you should switch off the printer and restart. Still if there is no progress, then call the Dell Printer Technical Support customer help desk of dell. They shall help you to resolve the issue.