Deinstall the OEM audio codec. Then reboot Reinstall the audio codec Reboot it will again "see" the audio jacks  
A couple of days ago, the front 3.5mm audio jack on my XPS 8940 stopped recognizing any device plugged into it.  I've tried 3 different headphones which all work in other devices.  The rear 3.5mm green audio jack still operates and so does the rear black 3.5mm jack.  How do I get the front jack operational again?
Front 3.5mm Audio Jack No Longer Recognizes headphones