I'm wondering if something in your autoplay settings has been altered. Have you checked in autoplay to see. Looking at mine, under devices I have none listed because I have none attached. Is the box ticked to use autoplay for all devices? Attach your device and then check and changes settings accordingly.
Does Device Manager detect any sort of device as being connected? Some mobile devices can change their USB mode for connecting to a computer (used for service staff on warranty repairs, etc)