Sorry to necropost but in case others are wondering about:
it is possible that the OP had a single combined headphone/microphone port (my current Laptop has one) and the 3.5mm plug has TWO rings and the microphone is wired between the ring furthest from the tip and the sleeve of the plug (How does vary! See:
https://en.wikipedia.org/wiki/Phone_connector_(audio)#TRRS_standards ). My current headphones have a built-in microphone and I had to get a splitter to go the other way on my previous laptop to separate the signals out to separate stereo plug for the headphones and a mono plug for the mic to plug into the separate sockets on that older unit.
