IHi,
see that you are having some issues when attempting to set HP Officejet Pro 8600 as default printer. You can try the following resolution.
1. Click Start, and then click Printers or Printers and Faxes or Devices and Printers. (Please take note that it depends which OS you are using. I am assuming you are familiar with Windows OSes).
2. If there is more than one icon in the folder for the printer, right-click the printer icon, and select Set as Default Printer.
While I am an HP employee, I am not a expert on all our products. If I offer advice, I'm not speaking for HP on how to solve an issue, but I'll do my personal best to help you. Was your question answered? Mark it as an Accepted Solution! See a great post? Give it a Kudos!