What could be stopping my WiFi printer from working?
One more thing you could try :


Uninstall all HP printer driver software using the HP uninstaller in Applications > Hewlett-Packard.
Reboot / restart your mac.
Reset the printing system via : Sys Prefs, Print &amp; Fax
Right (control) click in the rectangle listing your printers and then choose Reset Printing System.


CAUTION : The above steps will delete all of your printers.


Select the plus sign to re-add it. Look for the printer, select it and wait until the "Add" button becomes available. Click it.


Hope this helps.