1. Connect the printer to the computer and install the paper
2. Connect network cable to the printer and router
3. Press the wireless button present on the control panel
4. Download the HP Print and Scan Doctor
5. Run it from its location by clicking Downloaded file.
6. HP Print and Scan Doctor tool opens automatically and an icon is created on the desktop
7. Click start and select your printer
8. Click Next for a screen that will display the selected product and when it is not connected you can click on the connection type and give appropriate responses to the information on the screen
9. The printer should now come online
10. If HP Officejet Pro 8600 Offline issue not resolved, then close the Print and Scan Doctor tool first
11. When you click Fix Printing, new information will be updated on the screen
12. After reviewing the relevant information on the screen, you can respond to any of the actions that might require your attention
13. Now, clicking on Test Print will tell you if the printer is online
14. At this point, if a test page is printed, the Print and Scan Doctor window can be closed
15. When there is not output click No Print-> Continue -> Restart Computer
16. This should install all the additional updates.
Follow above steps to fix HP Officejet Pro 8600 Printer Offline Error.