Audio issues

I am experiencing a very strange problem.

I check out my audio before the meeting and everything is fine. When the meeting starts, however, the audio receive stops. the transmit seems to work still. Now what's truely wierd is that the receive comes through on my computer internal speaker. The volume level out of that is not sufficient and intelligibility suffers. Also the audio does not come through the front panel headphone jack.

I am baffled.

Help pleas.

Thanks in advance

Hank