Trouble with volume in Media Player when playing an Mpeg

I have a Dell laptop with Vista Basic. Pretty happy so far. When

attempting to play videos taked on our Sony Hardrive Handycam I can't get

any volume. The file is an Mpeg. I can get volume however when playing

them through thr Dell Media Center. I've checked all my volumes settings

and they are on/correct. I am able to play MP3 through WMP and get volume

but then tried a video to no avail. I do get video just no audio.

Any advice or hints?

Thank you