I have an HP LaserJet CP4005 printer with duplexing capabilities. I can not get the printer to duplex. I can not find anysetting on the printer menue to set it to duplex. I went in on the printer setup on the computer it's installed on and set it to 'print on both sides. Also I found in the preferences that it said Duplex not installed. the 'not installed' had a drop down and the other option was 'installed'. I set it to say duplex installed. Applied the settings, but nothing happened. Still printes on two pages instead of front and back. What can I do?