Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
That's a natural consequence of leaving an inkjet printer turned Off, with cartridges in it, for over a week or so. They should be left On, even if idle... occasionally, once or twice a day or so (depending upon exact model brand design etc.) they will waste a little ink, preventing the nozzles from clogging, when left On.
You will need to run a nozzle cleaning cycle - or, a 'cleaning' cycle, but not Roller Cleaning - from the Maintenance functions provided by your printers software - or, from the Maintenance menu on the printer, perhaps.
Then wait about 10 min. to an hour or so, to let the waste ink soak in.
Then run another nozzle cleaning or Head Cleaning cycle.
Then wait a few minutes, then run a third cleaning. After that, you will probably see the colors all come out fine, including black, I hope.
Let me know how it goes, please. Thanks.