Can't do voice chat when in chat room?

i don't understand why i can't use voice chat when in a chat room or a conference. i can hear the talking but just not able to talk. i use to be able to but want to know why i can't. when i voice chat one on one it's not a problem or when i i make pc to pc calls. i have a headset and i know the mic works fine but just having problems with it in chat. please help me.

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Your saying you cannot use voice chat in the chat room. Have you got external speakers mounted on each side of your monitor? If you got external speakers, Do you have them turned on to be using for that particular service that you are trying to use? And check at the bottom of your screen where there is a button for the volume control button in the task bar at the bottom. Let me know if this working for you. Try to double left click on the speaker button in the task bar at the bottom and should bring up a volume control settings. I hope this helps you.