My Samsung CLP-680ND Color Laser Printer suddenly reported a low color toner alert, and it brought the whole printer down--I was unable to print even black & white prints using the black toner.
To keep the printer working even when toner is low, disable the "TonerLow Alert" by going to (Menu) > System Setup > Maintenance > TonerLow Alert on the control panel.
Also, I don't recommend buying random toner on eBay, even if you get something that looks genuine in the mail. I ordered Cyan, Magenta and Yellow toners from eBay, and when installed, the printer complains that they aren't compatible. Get the real stuff from a reputable dealer.