Hi,
Try this: Power off the printer. Remove the power cable for more then 10-15 min. Remove the cartridge. Check it well. You must have a small board with golden pins on it (usually 4 pins). From this place the printer communicate with the cartridge (in the cartridge you have a small board with a memory i.c).
If this not help you'll need a specialist. The problem can be in the printer and/or in the cartridge (more probably in the cartridge).
Regards.