Microphone directed to Speakers
I had this problem and search the web but came up with nothing. A related question was whether it was possible to redirect a microphone directly to your speakers in order to use you computer as a PA. I am posting this because I couldn't find the correct answer to either question anywhere.
1. Go to you audio icon and select "Open Volume Control"
2. Select "Options" then "Properties"
3. There three possible selections: Playback, Recording and Other.
4. If you are having problems because your microphone is getting redirected to your speakers all the time then select "Playback" and simply Mute the Microphone.
5. To confirm that your microphone and speakers are setup correctly go back to the Audio Icon again and select "Adjust Audio Properties"
6. Select the Voice Tab and then select "Test hardware"
Follow the instruction and you will see that the microphone is still working because the test will connect the "RECORD" microphone to the speakers to check the volume.
So the answer to the second question of whether you can use your computer as a PA, is to simply not mute the microphone under Playback and then everything that is picked up by the microphone will be sent to the current speaker system.
I hope this helps