Hi there! My name is***** am a computer professional with over 15 years of experience with both Mac and Windows computers, phones, tablets, and printers. It would be my pleasure to assist you with this. This is a common problem with ink jet printer that are not used frequently. The ink that is left in the nozzles can dry up and clog the nozzles. Please give me just a moment to research cleaning procedures for your printer.
To clean the printhead on your HP Photosmart 7510 from the printer display
1. From the Home screen on the printer, press the Settings button. The Setup Menu is displayed.
2. In the Setup Menu, touch the screen to highlight Tools. Press OK.
3. Touch the screen to highlight Clean Printhead. Press OK.
Please allow the the cleaning procedure to complete. If it still doesn't print black correctly, run the cleaning cycle again. If you have done 2 cleaning cycles with no improvement, I suggest that you switch off the machine, wait 24 hours, and then perform Printhead Cleaning again. This will give the dried ink time to soften, and often resolves the issue.
Please give this a try and let me know how it works for you. If this solves the problem, would you mind taking a moment to rate my service? You can give your rating by selecting the stars located on the top right of the question page. I'd really appreciate it! Without a positive rating I am not credited for my answer. If this doesn't solve the problem be sure to let me know so we can continue troubleshooting.