My yahoo messenger voice call pc-pc working but the other side can never hear me! But if I use skype no problem. It used to work but may be because I changed my wireless router to Belkin! But I also turned off Belkin firewall settng... Still same problem. Any idea?

Try running through your settings again
Typical audio set up

Laptop with mic x webcam with mic x Vista x Yahoo Messenger 10
If you have an earlier OS, you may have to access your hardware from the Control Panel.

TEST SPEAKERS
Right click on speaker icon in System Tray or from Control Panel
Select "Playback Devices"
The speaker icon ( checked as working) and volume level graph should be visible
Right click on the volume graph and click "Test"
Left hand speakers followed by right hand should be heard

SET DEFAULT & TEST MIC
Click "Recording" tab.
To set required (webcam) mic as default - click on mic font to highlight and click "Properties"
In lower dropbox display "Use this device enable" click 'OK'
Click "Levels" tab and ramp up sliders ( adjust to suit later)
Return to "Recording". Test mic by speaking and make sure volume graph displays

Restart computer

CONFIGURE TO MESSENGER

Open messenger - on top toolbar. Left click ( > ) Messenger > Preferences > Connection - Select 'no proxies' or 'connect direct to the internet' depending on the version of messenger you have
make sure your internet connection and country are correct in the lower two boxes > Apply > OK

Click ( > ) Messenger > Preferences > Video and Voice
Set webcam mic and speakers to show Default equipment
Open Video and Voice Setup to test audio equipment
Click 'Place a free test call'
Check box 'Allow USB devices to access Messenger'
Click 'Apply' click 'OK'