Anyone had experience on this one?

Just bought a Optura300 from BH. the reason I choose it is because it can
recore MPEG4 clips. so the first thing I try is MPEG4 recording on SD card.
recorded a 40 sec clip, replayed it on camera it self, everything seems fine.
when I download it to my PC, I can see videos, but there's no sound. I'm
using windows media 9.0, with latest direct X. windows XP. I also send the
clip to my friend, same thing, they can see video but no sound. anyone
have any experience on this???????????

Weird, weird, weird --- i seem to have latest Windows Media Players, yet on my Mac OSX.3.9 machine i can hear audio but no video. On my Windows XP computer, I get video but no audio. Anyone else solved this problem? Found the right codecs?