Audio problem in downloaded videos from camcorder

I am trying to download and edit videos from Sony DCR-SR30E camcorder to Vista Home Premium edition. I downloaded videos either directly from hard disk of camcorder or via ‘Picture Motion Browser’ software which is provided by Sony. When I played videos through Sony software picture and audio seems ok. When I try to play the movie in Windows Media Player or import to Windows Movie Maker there is no audio. The version of Windows Media Player is 11.0.6000.6336 and it is supposed to have all necessary codecs. Any idea about the solution? Thanks in advance.