Assuming that your upgrade went smooth, otherwise; I would suggest that you completely remove and reinstall 'hplip'. Also delete any hplip and cups (dot).files you may be having. Then search for any remaining 'hp' in your 'file system' using
and delete them, if you find any.
Then check for Repositories using Synaptic and see if you have all the requisite repositories/sources enabled. If you are in doubt use this online tool to regenerate the repos, copy/paste the generated 'sources' into /etc/apt/sources.list using:
(You may have to enable 'Universe', 'Multiverse' and 'Backports' sources ).
$sudo gedit /etc/apt/sources.list
Then 'apt-get update'.
Having satisfied yourself, you can move on to reinstall 'hplip' and 'hplip-gui'. (use Synaptic to see if cups or hp backend is installed). Make sure your printer is switched on and connected before you run the hplip-gui/ device manager.
You must also set your printer as 'default printer' from System Settings- Printers.