problem with internal microphone

Hi there,

I am working with an IMAC and MAC OS 10.6.8

I presently encounter a problem with my internal microphone which does not seem to work.

I checked the settings under "sound" and tried a third party recording software.

I did not get any signal as "input" for internal microphone.

Then I tried an external microphone that is on a headset and plugged the usb connection. Then the signal went through.

Someone told me that I amy have a software problem with sounds settings and suggested that I should get rid of prefrences.

I did not find the pref for sound and I am afraid doing something wrong.

Could someone please help me

Many thanks in advance

Ivan