I just changed my toner cartridge and now it prints black

Check the toner cartridge to see if there is still a sheet of paper wrapped around the imaging drum, this paper is used to protect the imaging drum from damage in shipping. If the toner cartridge is spilling toner then you should return the cartridge as defective.

If the toner cartridge looks OK, try an interrupted print. Print a test page and open the top when the print job is about half way. Remove the partially printed paper and look if the print is all black, then look at the imaging drum on the toner to see if there is any print. If it is all black then it is either a defective toner cartridge or a problem with the high voltage power supply. Check the contacts on the toner cartridge and in the printer, sometimes the contacts get bent out of position.