How can I fix my HP 690C Deskjet printer to print in color? ?

My HP 690C Deskjet Printer's color cartridge refuse to print.I also bought a new color cartridge to solve the problem but it refuse to print in color. The black ink cartridge is printing well.
It seems that the cartridge assembly is not working properly and that it must be replaced with a new one.If so, where can I get a replacement for it and how can I take out the old one and replace it with a new one?