HP Officejet Pro 8600 Offline
Go to Settings on your computer & click Devices and Printers.
Choose Printers and Faxes, select View and click Details.
Right click on the printer and choose Details.
Check the connection status, if it is offline, right click on the printer and select Use HP Officejet Pro 8600 Printer Online.
Now try printing a document to verify the connection status.