Hi,
From the start menu click on Programs and select HP, next select the HP Officejet Pro 8600 folder and follow the Uninstall.
Next download and install the following software, do not use any older software from the CD or a software you may saved from the HP site in the past as the issue will remain while any previous software being used:
Once you are done, reboot your PC and click the HP Officejet Pro 8600 icon, located on your desktop.
Please let me know the results,
Shlomi