Hi SWAbbott,
Welcome to the HP Forums, I hope you enjoy your experience! To help you get the most out of the HP Forums I would like to direct your attention to the HP Forums Guide First Time Here? Learn How to Post and More.
Sorry to hear that you are having issue with printing in grayscale. Please do a complete uninstall of the software and drivers. Please be sure to remove the usb cable from the printer and the computer and lay it aside. The installation will let you know when to reconnect the usb cable. I am going to give you the link for the HP Photosmart and Officejet Full Feature Software and Drivers.
Please let me know if the troubleshooting steps I gave you do not resolve the issue.
Thank you.