Make sure your mic isn't muted, and that you have UPnP enabled. Also, double check your settings to make sure that the Kinect mic is being used when you're in Parties and Private Chat.
Did this solve your problem?
Sorry this didn't help.
Great! Thanks for marking this as the answer.
How satisfied are you with this reply?
Thanks for your feedback, it helps us improve the site.
How satisfied are you with this response?
Thanks for your feedback.