Why my printer wont print black?

Perhaps your black ink cartridge is empty? perhaps the nozzles from the print head are blocked, or sometimes just an air bubble in the head, between the cartridge and the nozzles have the same effect.
Also check if nothing os blocked under the print head. Dust or some scraps of paper.
When you are sure you have a filled original ink cartridge in the printer, try to run the clean print head program.
If one or two runs, still don't give any improvement, you could try to clean the head somewhat more drastic.
For that remove the printhead, and look in the place where it was. You se a small nozzle on the bottom. Just one or twe drops of cleaning fluid in the nozzle and start printing again.
This time just send some text pages to the printer and keep on putting the same pages in, till the printer starts printing.
The cleaning fluid comes with packages for refill cartridges or you can get some in an ink shop.