mic not working with ac97 sound card

i recently purchased a navtech headphone to chat with my friends...but seems that the microhpone does not seem 2 work...i am having AC97 ONBOARD sound card...the mic is fine as i have tried it on other computers....what could be the problem? i even tried re-installing vista..but still nothing happened...is there some problem with the jack..i'm plugging it in the correct jack...i am trying iwth both the mic and the headphone cables attached...i am also having a pinnacle tv tuner which is also detected as a recording device...it does not work on xp also
*img442.imageshack.us/img442/4807/captureze5.jpg