External Microphone not working under Windows

Hello guys,

i have this headset (without USB connector): http://europe.beyerdynamic.com/shop/hah/headphones-and-headsets/gaming/mmx-300.h tml

and a adapter that allowes unifies the two 3,5mm connectors (3 pin) to a single 4 pin connector.

under mac os x everything works fine: headset and microphone work excellent.

but other situation under windows: only headphones work, external microphones don't.

i think this has something to do with the audio driver but even after hours of research i have not found any solution for my problem.

any ideas?